Synthetic Explorations in the Pursuit of a Rapid, Photoactivatable, Nitroxyl

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SYNTHETIC EXPLORATIONS IN THE PURSUIT OF A RAPID, PHOTOACTIVATABLE NITROXYL DONOR

A thesis submitted to the Kent State University Honors College in partial fulfillment of the requirements for Departmental Honors

Mark Wesley Campbell

April, 2017

Thesis written by

Mark Wesley Campbell

Approved by

______, Advisor

______, Chair, Department of Chemistry & Biochemistry

Accepted by

______, Dean, Honors College

TABLE OF CONTENTS

LIST OF FIGURES……………………………………………………...….……………vi

LIST OF TABLES………………………………………………………………………..ix

ACKNOWLEDGMENTS…………………………………………………...... x

CHAPTER

1. INTRODUCTION...... 1

1.1 Chemical Properties of Nitroxyl ...... 2

1.1.1 Acid/Base Chemistry of Nitroxyl ...... 2

1.1.2 HNO Dimerization ...... 3

1.1.3 HNO Thiophilicity ...... 3

1.1.4 Nitroxyl Coordination Chemistry...... 4

1.1.5 Nitroxyl’s Reactions with Biomolecules ...... 5

1.2 Biological Properties and Therapeutic Uses of HNO ...... 6

1.2.1 Nitroxyl as a Vasorelaxant ...... 6

1.2.2 Nitroxyl as a Positive Inotrope ...... 8

1.2.3 Pharmacology of HNO ...... 8

1.2.4 Endogenous Production of HNO ...... 9

1.3 Detection of HNO ...... 12

1.3.1 Copper-based HNO Probes ...... 12

1.3.2 TEMPO HNO Probes ...... 12

iii

1.3.3 Phosphine-based HNO Probes ...... 13

1.3.4 Electrochemical HNO Detection ...... 13

1.4 HNO Donors ...... 14

1.4.1 Angeli’s Salt...... 14

1.4.2 Diazeniumdiolates...... 15

1.4.3 Acyloxy and Acyl Nitroso Compounds ...... 16

1.4.4 Protected Hydroxylamines ...... 17

1.5 HNO Donors Developed by the Sampson/Seed/Brasch Group .....19

1.5.1 Design of Photoactivatable HNO Donors ...... 19

1.5.2 First Generation 3,2-HNM HNO Donors ...... 21

1.5.3 Strategies for the Improvement of First-Generation Donor 24a ....25

1.6 Thesis Project Goals ...... 28

2. RESULTS AND EXPERIMENTAL DISCUSSION ...... 29

2.1 Primary Objectives...... 29

2.2 Synthesis of Secondary Alcohol Intermediate 32 ...... 29

2.3 Exploration of the Mitsunobu Reaction ...... 30

2.3.1 Initial Optimization of the Mitsunobu Reaction of Alcohol 32 .....30

2.3.2 Mitsunobu Reaction with a 2,6-disubstituted Analog of 32 ...... 33

2.3.3 Alternative Methods: Oxaziridine Amination ...... 34

2.3.4 Literature Regarding Mitsunobu Reaction of Sterically Hindered Alcohols ...... 37

2.3.5 Detailed Exploration of the Mitsunobu Reaction ...... 45

2.3.6 Synthesis of New NHPs ...... 51

2.6 Synthesis and Analysis of Donor 36 ...... 56

2.6.1 Completion of the Synthesis of Donor 36...... 56

2.6.2 Photochemical Analysis of Potential HNO Donor 36 ...... 59

2.7 Future Goals ...... 62

3. EXPERIMENTAL DETAILS ...... 64

3.1 General procedures ...... 64

3.2 Experimental details...... 66

REFERENCES ...... 115

NMR Spectra ...... 122

LIST OF FIGURES

Figure 1.1: Lewis structure of nitroxyl ...... 1

Figure 1.2: The dimerization/degradation of HNO...... 3

Figure 1.3: The reactions of HNO with thiols ...... 3

Figure 1.4: The reactions of HNO with metals ...... 5

Figure 1.5: HNO production from cyanamide in a biological system ...... 9

Figure 1.6: Biosynthesis of HNO from the NOS intermediate: N-hydroxy-L-arginine ....10

Figure 1.7: Reaction of NO with thiols with possible HNO intermediacy ...... 10

Figure 1.8: Production of HNO from NOS and CBS products with subsequent TRPA1 activation ...... 11

Figure 1.9: Mechanism of electrochemical HNO detection via cobalt porphyrin ...... 14

Figure 1.10: The aqueous degradation of Angeli’s salt ...... 14

Figure 1.11: Structures of various diazeniumdiolates ...... 15

Figure 1.12: Hydroylsis of acyloxy nitroso compounds to release HNO ...... 16

Figure 1.13: Mechanism of HNO release from donors developed by King’s group ...... 17

Figure 1.14: Mechanism of HNO release from PA ...... 18

Figure 1.15: Acidity constants and HNO release rates for various PA analogs ...... 18

Figure 1.16: HNO donors developed by the Toscano group ...... 19

Figure 1.17: HNO donor using a photolabile (3-hydroxy-2-napthyl)methyl (3,2-HNM) protecting group ...... 20

Figure 1.18: Mechanism of 3,2-HNM photocleavage ...... 20

Figure 1.19: Synthetic scheme for the preparation of first-generation HNO donors ...... 21

Figure 1.20: 19F NMR spectra monitoring the progress of the photolysis of donor 24a ...22

Figure 1.21: Proposed mechanism for the generation of the two observed products from the photodecomposition of donor 24a ...... 23

Figure 1.22: Base-mediated decomposition of 24d ...... 24

Figure 1.23: UV-Vis spectra showing the reaction of HNO with H2OCbl(III) ...... 25

Figure 1.24: Incorporation of a benzylic substituent as a potential strategy to improve selectivity for HNO generation ...... 26

Figure 1.25: Synthetic scheme for the preparation of donor 39 ...... 26

Figure 1.26: Products of the LiAlH4 reduction of ester 18 ...... 27

Figure 2.1 Preliminary steps in the synthesis of donor 36 ...... 30

Figure 2.2: Attempted acid-catalyzed substitution of 32 ...... 33

Figure 2.3: Mitsunobu reaction of (-)-menthol with benzoic acid ...... 33

Figure 2.4: Synthetic preparation of 2,6-disubstituted analogs ...... 34

Figure 2.5: Proposed mechanism of alcohol amination via oxaziridine ...... 35

Figure 2.6: Preparation and application of Ellman’s oxaziridine ...... 36

Figure 2.7: Mitsunobu esterification of sterically hindered alcohols with chloroacetic acid ...... 40

Figure 2.8: Mechanism of the Mitsunobu esterification ...... 40

Figure 2.9: Brønsted plot of log k vs pKa illustrating the rates of alcohol activation and SN2 reaction with various carboxylic acids ...... 43

Figure 2.10: Side reaction that occurs when the alcohol is omitted from the Mitsunobu reaction ...... 44

Figure 2.11: Preparation of phthalimides from the corresponding anhydride via base- mediated hydroxylamine substitution ...... 46

vii

Figure 2.12: Scheme for one-pot preparation of NHPs from corresponding phthalimides ...... 47

Figure 2.13: Preparation of secondary alcohols 71a-d with various protecting groups ....48

Figure 2.14: Calculated cone angles and lowest energy conformation structures for each secondary alcohol substrate (71a-d) ...... 49

Figure 2.15: Isolated yields of Mitsunobu reactions with NHP and alcohol substrates ....50

Figure 2.16: Isolated yields for Mitsunobu reaction with EWG-substituted NHPs ...... 51

Figure 2.17: General catalytic cycle for palladium-catalyzed carbonylative coupling leading to phthalimide 82...... 53

Figure 2.18: Proposed method for the preparation of EDG-substituted NHPs from aryl dihalides ...... 53

Figure 2.19: Preparation of PMB-dimethoxy NHP (73) via aryl diiodide 72 ...... 55

Figure 2.20: Preparation of PMB-dimethoxyl NHP (73) via aryl dibromide 74 ...... 55

Figure 2.21: Final steps in the synthesis of donor 36 ...... 56

Figure 2.22: Cleavage of the NHP motif to yield alkoyamine 76 ...... 56

Figure 2.23: Sulfonylation of alkoxyamine 88 with triflic anhydride ...... 58

Figure 2.24: Proposed mechanism for sulfonylation/MOM-deprotection to produce donor 36...... 59

Figure 2.25: 19F NMR analysis of the photodecomposition of donor 36...... 60

Figure 2.26: Proposed mechanism for photodecomposition of donor 36 ...... 61

Figure 2.27: Comparison of photolysis product ratio for donor 36 vs. donor 24a ...... 61

viii

LIST OF TABLES

Table 1.1: Estimated rate constants for reactions of HNO with select biomolecules ...... 5 Table 2.1: Preliminary trials of various conditions for the Mitsunobu reaction ...... 32 Table 2.2: Mitsunobu reaction of (-)-menthol with various benzoic acids ...... 39 Table 2.3: Ratio of products in the alcohol-free Mitsunobu reaction ...... 44

ACKNOWLEDGEMENTS

I would like to begin by thanking my family. My mother, Laura Campbell, has provided unwavering love and emotional support for me throughout my entire life. During my education she has been a constant source of encouragement regardless of the circumstances. I want to thank my father, Brian Campbell, for instilling in me a healthy work ethic and the value of education. His continual willingness to teach and assist me in any situation has been invaluable. Both my mother and father have provided me with paramount examples of diligent, godly and caring parents. In addition, my sisters, Kristen

Newman and Jennifer Siegel, have always encouraged me to strive for excellence and helped instill confidence in me.

I would also like to thank all the faculty members in the Department of Chemistry at Kent State University for providing me with a quality education in chemistry. I would like to specifically thank my advisors, Drs. Paul Sampson and Alexander Seed. These gifted men have guided me throughout my research experience and skillfully instructed me at the onset of my career in science.

Finally I would like to thank all of the members of the Sampson/Seed group for their support, guidance and advice throughout my research project. A special thanks to Dr.

Scott Bunge and Julian Sobieski for performing the Tolman cone angle calculations.

CHAPTER 1. INTRODUCTION

In 1998 three scientists, Robert F. Furchgott, Ferid Murad, and Louis J. Ignarro, were awarded the Nobel Prize for their research on the pharmacology of nitric oxide. They found that nitric oxide was an important biological signaling molecule in mammals and described several physiological mechanisms of action for nitric oxide. Nitric oxide is known to play a critical role in vascular homeostasis, platelet aggregation, inflammation, angiogenesis and fibrinolysis.1 These discoveries sparked interest in the study of other

- - molecules closely related to nitric oxide, including peroxynitrite (ONOO ), nitrite (NO2 ),

- nitrate (NO3 ), nitrogen dioxide (NO2) and dinitrogen trioxide (N2O3). Nitroxyl (HNO, nitrosyl hydride or azanone) (Figure 1.1), the one-electron reduced and protonated sibling of nitric oxide, has received much less attention. However, it has been recently reported that nitroxyl has several chemical and biological properties that differ significantly from nitric oxide.2

Figure 1.1: Lewis structure of nitroxyl

1.1 Chemical Properties of Nitroxyl

1.1.1 Acid/Base Chemistry of Nitroxyl

This simple, triatomic molecule has a surprisingly broad range of unique chemical properties. Initial studies reported that nitroxyl was a relatively strong acid (pKa = 4.7) and would exist predominantly as its conjugate base, NO-, under physiological conditions.3

However, more recent experiments have shown that nitroxyl is much less acidic (pKa

~11.4), suggesting that HNO is the most prevalent species in aqueous solution at neutral

4 pH. Even with the correct measurement of acidity, the Ka of nitroxyl does not accurately describe the ratio of HNO:NO- in physiological systems. Normally, proton transfer between an acid and conjugate base is so rapid that the Ka is an accurate estimate of their respective equilibrium concentrations. However, the electronic ground states of HNO and NO- differ

(HNO = singlet and NO- = triplet), making the deprotonation reaction spin-forbidden by quantum mechanics.6 Such spin-forbidden processes are less kinetically favorable than spin-allowed processes and, thus, occur at a slower rate. Given this unusual aspect of nitroxyl’s acid/base chemistry, it is expected that reactions other than deprotonation will occur at a faster rate and be more prevalent. Also noteworthy is the atypical N-H bond strength in HNO. The N-H bond energy in HNO is only 49.9 kcal mol-1, significantly lower than the average N-H bond energy (~90 kcal·mol-1). Thus the N-H bond of HNO is particularly weak and can be broken more easily than typically N-H bonds.6

1.1.2 HNO Dimerization

Perhaps the most prevalent reaction of HNO is its spontaneous dimerization/degradation (Figure 1.2). This decomposition reaction is exceedingly rapid with a second order rate constant of 8 × 106 s-1M-1.5 This inherent instability provides a challenge when studying the biological and chemical properties of HNO and necessitates the use of HNO donor molecules.

Figure 1.2: The dimerization/degradation of HNO

1.1.3 HNO Thiophilicity

One of the most significant properties of nitroxyl is its propensity at act as an electrophile. Though relatively unreactive toward water and alcohols, HNO is highly thiophilic.4 The reaction of nitroxyl with thiols has multiple outcomes depending upon the nature and concentration of the thiol (Figure 1.3).7

Figure 1.3: The reactions of HNO with thiols

Initial attack of the nucleophilic sulfur on HNO results in the formation of an N- hydroxysulfenamide intermediate (1). This intermediate may be consumed with another

equivalent of thiol producing the corresponding disulfide (2) and hydroxylamine.

Alternatively, the N-hydroxysulfenamide may undergo isomerization to form a sulfinamide

(3). In biological systems, the reaction of the N-hydroxysulfenamide to form the disulfide is reversible, while rearrangement to the sulfinamide is not. Both of these reactions have been demonstrated to play an important role in alteration of protein structures by HNO, such as during the inhibition of alcohol dehydrogenase via cyanamide.8

Though direct experimental investigation is lacking, it is likely that HNO also functions as an electrophile in the presence of amine nucleophiles. Theoretical calculations by Bartberger et al. suggested that the nucleophilic addition of amines to HNO would be highly thermodynamically favorable.4 Some reports predict that other nitric oxides may provide an additional route for HNO consumption in biological systems.5

1.1.4 Nitroxyl Coordination Chemistry

Nitroxyl also has extensive coordination chemistry with biological relevance.

Hemoglobin, myoglobin, cytochromes and other metalloproteins are all major biological targets of HNO.2 It has been demonstrated that HNO can react with iron, copper and manganese centers in porphyrins, corroles, and corrines via reductive nitrosylation to produce a metal-nitrosyl adduct (Figure 1.4, Reaction 1).9 Reductive nitrosylation via

HNO has been demonstrated with a variety of ferric centers including horseradish peroxidase, cytochrome c, methemoglobin and myoglobin.10 Conversely, HNO can oxidize metal-oxygen species, such as oxymyoglobin, although the exact mechanism for this reaction has not yet been elucidated (Figure 1.4, Reaction 2).11 Though most HNO-metal

complexes are unstable (due to facile oxidation to NO), HNO can associate with ferrous myoglobin producing an unexpectedly stable complex (Figure 1.4, Reaction 3).12

Figure 1.4: The reactions of HNO with metal complexes 9

1.1.5 Nitroxyl’s Reactions with Biomolecules

Given the range of species that react with nitroxyl, a comparison of rates would be necessary to determine the most prevalent biological reactions of HNO. Miranda and coworkers published a report detailing the rates of reaction of nitroxyl with biological targets which are summarized in Table 1.1.10

Table 1.1: Estimated rate constants for reactions of HNO with select biomolecules 10

Estimated rate Biomolecule constants (k, M-1s-1) Oxymyoglobin 1 × 107 Glutathione 2 × 106 Horseraddish peroxidase 2 × 106 Metmyoglobin 8 × 105 Cu/Zn superoxide dismutase 7 × 105 N-acetylcysteine 5 × 105 Catalase 3 × 105 Fe3+ cytochrome c 4 × 104 3 O2 3 × 10

This table illustrates the significant effects of protein environments on the rate of

HNO reactivity. Nitroxyl’s reaction with cytochrome c requires the displacement of an

axial ligand of Fe3+ (either histidine 18 or methionine 80),13 making it significantly slower than the reaction with metmyoglobin, which has an open binding site.10 Importantly, the relatively slow rate of nitroxyl’s reaction with molecular oxygen suggests that oxidation to reactive peroxides is unlikely to occur in physiological systems. This attribute of nitroxyl is a key distinction from the chemistry of nitric oxide, as NO will react with oxygen to form higher oxidation species which are often cytotoxic.

1.2 Biological Properties and Therapeutic Uses of HNO

The therapeutic potential of nitric oxide in the treatment of cardiovascular disease stems from its ability to increase the rate of myocardial relaxation (positive lusitropy).

However, the therapeutic efficacy of nitric oxide donors is limited by tolerance development, decreased effectiveness under oxidative stress and potential cytotoxicity.2

Researchers have also demonstrated nitroxyl’s ability to act as a potent vasorelaxant and to increase myocardial contractility (positive inotropy).14 Nitroxyl’s mechanism of biological activity is unique and may be able to overcome the limitations encountered in the clinical use of nitric oxide donors.

1.2.1 Nitroxyl as a Vasorelaxant

Experiments with conscious dogs revealed that intravenous administration of an

HNO donor, Angeli’s Salt (AS), increased end systolic chamber stiffness (related to contractility) with rapid ventricular relaxation.15 In failing hearts, HNO was shown to increase the rate of myocardial contractility while improving relaxation. Neither of these

effects could be replicated in failing hearts with nitric oxide donors, such as diethylamine

NONOate. Importantly, nitroxyl’s effects were not suppressed by repression of β- adrenergic signaling.16 Activation of the β-adrenergic receptors is a common response of the sympathetic nervous system to increase cardiac output. However, it is well-documented that the β-adrenergic pathway is greatly impaired during heart failure. This independence from the β-adrenergic pathway makes nitroxyl an attractive agent for cardiac regulation during heart failure.17 These intriguing therapeutic effects warrant extensive study of

HNO’s biological mechanisms of action.

It has been shown that HNO induces vascular relaxation via activation of soluble guanylyl cyclase (sGC), a heme-centered protein complex essential for vasodilation. Upon activation sGC increases cellular cyclic guanosine monophosphate (cGMP) concentrations which, in turn, activate voltage-gated potassium channels (Kv) leading to a hyperpolarization of vascular smooth muscle cells. However, full details of these mechanisms are not yet fully understood.9 Whether the activation of sGC occurs in the Fe2+ state via NO (presumably produced from the oxidation of HNO) or if HNO directly reacts with the ferric sGC is still debated.2,4 Discrepancies in the role of calcitonin gene-related peptide (CGRP) further complicate the mechanism of vasodilation.2,9 CGRP is a neuropeptide known to increase vascular smooth muscle cyclic adenosine monophosphate

(cAMP) concentrations and activate Kv channels to evoke vasodilation. Various studies have demonstrated that AS increases plasma levels of this neuropeptide. Surprisingly, application of CGRP8-37, a CGRP antagonist, after AS administration does not diminish vasodilation but rather affects the inotropic properties of HNO.15

1.2.2 Nitroxyl as a Positive Inotrope

One of nitroxyl’s most unique therapeutic effects is its ability to regulate myocardial contractility which is not observed with any other nitric oxides.9 Current positive inotropes have failed to provide long-term support for heart failure and are often harmful. Excitingly, HNO appears to operate via a mechanism independent and additive to traditional β-adrenergic signaling.16 Regulation of the myocardium appears to stem from

HNO’s ability to modify thiol moieties on ryanodine receptors (skeletal RyR1 and cardiac

RyR2) and calcium ion pumps on the sarcoplasmic reticulum. RyRs are responsible for the release of Ca2+ from the sarcoplasmic reticulum which then bind to troponin to facilitate muscle contraction.18 After muscle contraction, calcium is taken back in the sarcoplasmic reticulum via Ca2+ ion pumps. Nitroxyl seems to activate both of these components, causing an overall increase in calcium cycling which results in an increase in myocardial contractility.19

1.2.3 Pharmacology of HNO

These physiological effects and their distinctive mechanisms make HNO an attractive candidate for the treatment of heart failure. Currently, there are no pharmaceutical agents which utilize HNO for cardiac treatment. However, HNO is utilized in one well-known drug, cyanamide (aminomethanenitrile). In 1990, the Nagasawa lab demonstrated that cyanamide, used for the treatment of acute alcoholism, is actually a prodrug for nitroxyl. Oxidation of cyanamide (4) via hydrogen peroxide and catalase produces the transient N-hydroxycyanamide intermediate (5) which then decomposes to HNO and

hydrogen cyanide (Figure 1.5).20 Nitroxyl was demonstrated to be the agent which inhibited alcohol dehydrogenase via modification of the active-site cysteine thiolate.2 This drug is only approved in Canada, Europe and Japan due to side effects of alcohol ingestion after administration of cyanamide.

Figure 1.5: HNO production from cyanamide in biological systems 20

Importantly, recent developments have emerged in the clinical use of an HNO prodrug for the treatment of acute decompensated heart failure. Originally developed by researchers at Cardioxyl Pharmaceuticals, lead candidate CXL-1427 was acquired by

Bristol-Myers Squibb in 2015 and is now in phase II clinical trials (see section 1.4.4).

1.2.4 Endogenous Production of HNO

Given its potential as a biological signaling molecule, it seems likely that nitroxyl would be naturally produced in physiological systems, yet, direct evidence for the endogenous production of HNO remains elusive. Nitric oxide is produced enzymatically in biological systems via the oxidation of L-arginine by nitric oxide synthase (NOS) under

21 tetrahydrobiopterin (BH4)-deficient conditions. Oxidation of L-arginine (6) via NOS results in an intermediate, N-hydroxy-L-arginine (7). HNO can be generated from N- hydroxy-L-arginine, following its oxidation by peroxinitrate (ONOO-) (Figure 1.6).

During the production of NO, BH4 activates molecular oxygen via single electron transfer;

the resulting radical then oxidizes NOS leading to a ferric nitrosyl center releasing nitric oxide. Only in the absence of BH4, can HNO be produced with the stable, ferrous nitrosyl species.22 Although experimental observations validate this mechanism it remains to be seen whether nitroxyl is actually produced in vivo via this route.

Figure 1.6: Biosynthesis of HNO via the NOS-derived intermediate

N-hydroxy-L-arginine 21

Another assumed method for biological production of HNO involves the reaction of nitric oxide with thiols. Analogous to nitroxyl’s thiophilicity, reaction of NO with aromatic or aliphatic thiols yields a disulfide along with nitrous oxide, strongly suggesting the intermediate formation of HNO (Figure 1.7).23

Figure 1.7: Reaction of NO with thiols with possible HNO intermediacy

Reaction of nitric oxide with both hydrogen sulfide and albumin (a protein possessing several accessible cysteine thiol residues) produces N2O, suggesting a biologically relevant context for endogenous HNO formation.24 Reports have demonstrated that the previously well-known H2S-evoked vasodilation results from H2S production from

cystathionine beta synthase (CBS) and NO production from NOS. Anticipated formation of HNO from co-localized H2S and NO could then oxidize thiol residues on transient receptor potential channel A1 (TRPA1), which releases CGRP upon activation, ultimately leading to positive lusitropic effects (Figure 1.8).25 Independent experiments demonstrated nitroxyl’s ability to activate TRPA1, giving HNO a possible physiological role in myocardial function.15

Figure 1.8: Production of HNO from NOS and CBS products with subsequent

TRPA1 activation 25

Additionally, researchers have found evidence to suggest that HNO could be produced via the reaction of NO with alcohols, including hydroquinone, tyrosine, ascorbic acid and α-tocoferol. Experiments which infused bovine arterial cells with ascorbate showed evidence of HNO production via application of a fluorescent HNO sensor,

CuBOT1.26

1.3 Detection of HNO

One of the greatest challenges encountered in the study of nitroxyl involves its detection. Given the transient nature of HNO in aqueous solution, many traditional methods of analysis such as mass spectrometry, HPLC and electron paramagnetic resonance spectroscopy, have proved to be of limited value in HNO detection. In the past, detection and quantification of nitrous oxide, the main product of nitroxyl’s dimerization/degradation, was used in studies with HNO. However, a direct and simple method for HNO detection is necessary for both biological and chemical studies. To this end, a variety of fluorescent probes have been prepared which allow for detection of HNO.

There are three main classes of HNO-probes: copper-based probes, probes which utilize interactions of HNO with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and other nitroxide radicals, and phosphine-based fluorescent HNO probes.27

1.3.1 Copper-based HNO Probes

Copper-based fluorescent probes utilize the reductive nitrosylation that occurs when HNO reacts with cupric species. Most of these probes emit light from the visible to near-infrared region.27 Interestingly, some probes engineered by Lippard’s group have the ability to selectively detect HNO over NO in aqueous solution.28

1.3.2 TEMPO HNO Probes

TEMPO probes operate by abstracting the hydrogen atom from HNO, where the

N-H bond is significantly weaker than a typical N-H bond.6 Since NO lacks a proton, these

probes are highly selective for HNO; however, application in biological systems is hampered by the resulting highly reactive nitroxide radical species.29

1.3.3 Phosphine-based HNO probes

The reaction of HNO with organic phosphine species results in an azaylide and the corresponding phosphine oxide which provides fluorescence. There has been extensive research in phosphine-based fluorescent probes and these appear to be the most promising of the three classes.27

1.3.4 Electrochemical HNO Detection

Finally, an intriguing method for HNO detection using electrochemical methods was proposed by Doctorovich and coworkers. Electrochemical methods are among the most valuable for the trapping and detection of reactive, transient species such as nitroxyl.

Utilizing previously established methods for in vitro electrochemical detection, the

Doctorovich lab designed a cobalt-centered porphyrin to act as an electrochemical sensor

(Figure 1.9). This porphyrin monomer contains four thiol motifs to which a gold electrode is covalently linked. High selectivity for HNO over NO is achieved by maintaining the

CoIII oxidation state. While nitroxyl undergoes facile addition to cobalt(III) species, no such reaction is observed with nitric oxide. After reaction with HNO, the CoIII porphyrin probe undergoes oxidation, releasing current to the amperimeter. This electrochemical probe successfully gave quantitative measurement of HNO in solution at a wide range of concentrations.30

Figure 1.9: Mechanism of electrochemical HNO detection via cobalt porphyrin 30

1.4 HNO Donors

1.4.1 Angeli’s Salt

The most historic and popular nitroxyl donor is sodium trioxodinitrate, commonly referred to as Angeli’s salt (AS). Preparation of AS was first reported in 1896; however, its ability to donate HNO was not suggested until 1907.31 The exact mechanistic details of its aqueous decomposition have been elucidated more recently with the aid of theoretical calculations.32 AS is preferentially protonated at the nitroso oxygen. Tautomerization of the protonated species followed by heterolytic cleavage of the N-N bond then yields HNO and nitrite (Figure 1.10).

Figure 1.10: The aqueous degradation of Angeli’s salt 33

The decomposition of AS was determined to be first order and pH dependent. HNO release rates for AS are most efficient from pH 4-8 with an average half-life of ~3

minutes.33 Although it has been used in a variety of chemical and biological studies of

HNO, AS has two significant disadvantages. The production of HNO from AS yields an equivalent of nitrite which can have independent chemical and biological effects and can serve as a source of NO. Additionally, the rate of HNO release for AS is essentially fixed since modifications to the structure to create analogs are not realistic.

1.4.2 Diazeniumdiolates

Analogous to AS, diazeniumdiolates are a class of HNO donors which has been studied extensively. Primary diazeniumdiolates have a common structural motif (9) with variable R groups, the most common being the isopropyl analog (IPA/NO, sodium 1-(N- isopropylamino)diazen-1-ium-1,2-diolate) (Figure 1.11).

Figure 1.11: Structures of various diazeniumdiolates 35

These species undergo an HNO-releasing mechanism similar to that of AS.34

Primary diazeniumdiolates offer little variation in HNO-release rate (t1/2 = 2-6 minutes) and are hampered by their inherent instability with respect to tautomerization and nitric oxide release.35 Derivatization of primary diazeniumdiolates at O2 increases the stability of these donors and adds a trigger mechanism, such as ester hydrolysis, that offers control over HNO release. Such donors have been prepared and some show a propensity to serve as HNO prodrugs.36

1.4.3 Acyloxy and Acyl Nitroso Compounds

Acyloxy and acyl nitroso compounds are another set of HNO donors that have received significant attention. The King group reported acyloxy nitroso compounds that release HNO upon hydrolysis, producing the corresponding carboxylic acid and ketone as byproducts (Figure 1.12).37

Figure 1.12: Hydrolysis of acyloxy nitroso compounds to release HNO 37

This family of donors was based on a common cyclohexyl structure with variable acyl groups (R). Initial studies with the acetate ester released HNO in good yield but only in alkaline solution (0.1M NaOH in MeOH). However, the trifluoroacetate analog (R =

CF3) gave efficient HNO release in buffered (pH 7.4) solution and showed vasorelaxation similar to that of AS in rat aortic rings.

King’s group also examined the development of acyl nitroso compounds which could be triggered to release HNO using a retro-Diels-Alder reaction.38 Donors 10 and 11 thermally decomposed to form their respective acylnitroso compounds which then hydrolyzed to give HNO and corresponding byproducts in acetonitrile or water solutions at 37 °C (Figure 1.13). Donor 11 provided higher yields of HNO than 10 (86% and 42% respectively) with approximately a twofold decrease in half-life (t1/2 10 = 53 min; t1/2 11 =

24 min).

Figure 1.13: Mechanism of HNO release from donors developed by King’s group 38

Analogous to King’s donors, Nakagawa and coworkers prepared donors which undergo a retro-Diels-Alder reaction, producing an acyl nitroso intermediate which subsequently releases HNO.39 The Nakagawa group claimed that these caged donors are photoactivatable, releasing HNO upon irradiation. Though these molecules do exhibit controlled release of HNO, it is unlikely that the mechanism is photo-induced. As previously mentioned, retro-Diels-Alder reactions are known to be a thermally mediated process and are photochemically forbidden according to the Woodward-Hoffman rules.40

Additionally, it was found that HNO release continues after irradiation, consistent with a thermally-mediated HNO release mechanism.

1.4.4 Protected Hydroxylamines

Likely the most interesting group of HNO donors are N-substituted hydroxyl amines, the most renowned donor of this class being N-hydroxybenzenesulfonamide, commonly known as Piloty’s Acid (PA). Under alkaline conditions PA can serve as a

-4 -1 relatively rapid HNO donor (k = 4.22 × 10 s ) via deprotonation of the hydroxyl group

9 (pKa = 9.3) and subsequent elimination (Figure 1.14).

Figure 1.14: Mechanism of HNO release from PA

However, at physiological pH, PA can only serve as a NO donor. Thus, studies of

PA derivatives aim to modify the pKa of the hydroxyl proton, the efficacy of the leaving group or a combination of both. Indeed, the Doctorovich group prepared several PA derivatives which displayed a wide variety of hydroxyl pKas and HNO release rates (Figure

1.15).41

Figure 1.15: Acidity constants and HNO release rates for various PA analogs 41

The seemingly inconsistent relationship between pKa and rate constants suggests that both kinetic and thermodynamic effects contribute to HNO release, including, hydroxyl acidity, N-O bond length, steric crowding and stability of released sulfinate anions. Notably, Cardioxyl Pharmaceuticals developed an o-sulfonylmethyl derivative of

PA (CXL-1020) which was used to provide the first in-human results for the treatment of heart failure by an HNO donor.42 This lead candidate was recently acquired by Bristol-

Myers Squibb and has proceeded to phase II clinical trials.

Toscano and coworkers have explored related HNO donors based on a barbituric acid central motif.43 Donor 12 proved to give the highest percentage release of HNO with a half-life of 0.7 minutes in a phosphate-buffered saline (PBS) solution at pH 7.4. A pyrazolone-based donor (13) synthesized by this group also proved to be an effective HNO donor with a half-life of ~10 minutes at pH 7.4. Although their decomposition byproducts require pharmacological evaluation, donors 12 and 13 appear to be efficacious HNO donors with promise for physiological studies.

Figure 1.16: HNO donors developed by the Toscano group 43

1.5 HNO Donors Developed by the Sampson/Seed/Brasch Group

1.5.1 Design of Photoactivatable HNO Donors

As previously mentioned, the mechanistic details of nitroxyl’s reactions with metalloproteins are not yet fully understood. Such mechanistic and kinetic studies would require rapid (t1/2 << seconds), controlled and highly selective release of HNO. Although there have been a variety of different HNO donors developed, there are none that release

HNO on such a rapid time scale. A major goal of our research group is to develop such donors which would rapidly release HNO upon photoactivation.

Our initial design utilized the photolabile (3-hydroxy-2-naphthyl)methyl (3,2-

HNM) OH protecting group in conjunction with an N-sulfonylhydroxylamine head group

(Figure 1.17).

Figure 1.17: HNO donor using a photolabile (3-hydroxy-2-naphthyl)methyl (3,2-

HNM) protecting group

Though they are normally weak acids (pKa ~ 8-10), naphthols become significantly

44 more acidic when in an electronically excited state (pKa* ~ 2). Popik’s group reported

5 -1 that the 3,2-HNM group undergoes remarkably rapid photocleavage (krelease ~10 s ) with very efficient quantum yields (Φ = 0.17-0.26).45

The proposed mechanism is initiated by photodeprotonation of the naphthol followed by intramolecular cyclization, releasing the OR group. Electrocyclic ring opening of the benzoxete (14) affords an o-naphthoquinone methide intermediate (15) which rapidly reacts with water, yielding the corresponding diol (16) (Figure 1.18).

Figure 1.18: Mechanism of 3,2-HNM photocleavage 45

Based on Popik’s results, the 3,2-HNM group was considered to be a promising photoprotecting group for our donors because it could be rapidly cleaved at neutral pH in the absence of additional nucleophiles.

1.5.2 First Generation 3,2-HNM HNO Donors

Three first generation 3,2-HNM-based HNO donors (24a-c) were synthesized according to a common synthetic scheme (Figure 1.19).46

Figure 1.19: Synthetic scheme for the preparation of first-generation HNO donors 46

To begin the synthesis, commercially available methyl 3-hydroxy-2-napthanoate

(17) underwent phenolic protection using the triisopropylsilyl group (TIPS) in good yield.

Reduction of the protected ester (18) with lithium aluminum hydride provided only poor yields of the corresponding alcohol. The alcohol was easily brominated with phosphorus tribromide followed by base-mediated substitution using an N-hydroxyphthalimide (NHP) nucleophile. Completing this Gabriel-type synthesis, adduct 21 underwent reaction with hydrazine monohydrate to produce alkoxyamine 22 in quantitative yields. Sulfonation was performed with three different sulfonyl chloride reagents, producing adducts 23a-c in good

to moderate yield. Finally, fluoride-mediated deprotection was achieved with either tetrabutylammonium fluoride or potassium fluoride to yield the target HNO donors 24a-c.

The resulting donors were then subjected to photoirradiation. The rate of photodecomposition of donor 24a was determined via a stopped-flow kinetics instrument under strictly anaerobic conditions. A solution of donor 24a (80.0 µM) in a phosphate buffer (5 mM, pH = 7.00) and acetonitrile (40:60 v/v) was irradiated with a Xe light source

(150 W). The absorbance data was fitted to a first-order equation, giving a half-life of 50

-2 -1 seconds (kobs = (1.4 ± 0.1) × 10 s ) for donor 24a. More concentrated samples of donor

24a (1.00 mg, 3.89 mM) were prepared via the same procedure and used for further photolysis studies. The solution of 24a was transferred to an NMR tube, fitted with an air- tight cap and irradiated in a mini photoreactor (Rayonet RMR-600) with 350 nm bulbs (4

W, 8 lamps) for 35 min. The progress of the reaction was monitored periodically by 1H or

19F NMR spectroscopy throughout the irradiation (e.g. Figure 1.20). Based on the 19F

NMR spectrum below, two fluorinated species were formed during the reaction:

- CF3SO2NH2 and CF3SO2 (Figure 1.20).

Figure 1.20: 19F-NMR spectra monitoring the photodecomposition of donor 24a 46

- The integration ratio between CF3SO2NH2 and CF3SO2 was approximately 40:60.

The formation of these products can be rationalized by two competing reaction mechanisms outlined in Figure 1.21.

The HNO-generating reaction (Figure 1.21, Pathway A) proceeds via photodeprotonation of the electronically excited naphthol. The resulting excited anionic species (25) then undergoes a concerted elimination, expelling both HNO and the observed sulfinate byproduct. The corresponding naphthoquinone methide (26) readily undergoes conjugate addition with water to form diol 27. It was also observed that donor 24a could undergo a competing photoredox reaction described by Pathway B (Figure 1.21). We speculated that intramolecular hydrogen bonding of the naphtholic hydrogen with the lone pair on nitrogen can form a seven-membered ring which may facilitate a solvent-mediated elimination producing the observed CF3SO2NH2 in addition to aldehyde 30. In addition to

19 - F NMR detection of the two fluorinated species, CF3SO2NH2 and CF3SO2 , the production of diol 27 and aldehyde 30 were confirmed via 1H NMR spectroscopy.

Figure 1.21: Proposed mechanism for the generation of the two observed products

from the photodecomposition of donor 24a 46

Further confirmation for the concerted nature of the photolytic elimination was provided by analysis of trifluoromethyl derivative of N-hydroxymethanesulfonamide

(24d).47 This molecule conveniently served as the parent HNO donor motif without the 3,2-

HNM photoprotecting group. Under basic conditions, donor 24d undergoes the elimination reaction described in Figure 1.22 to produce HNO and triflinate.

Figure 1.22: Base-mediated decomposition of 24d 47

If the photodecomposition of donor 24a proceeded via a stepwise elimination, an appreciable amount of fragment 24e would accumulate and be detected by 19F NMR analysis. However, no evidence for the production of intermediate 24e was found in the

19F NMR spectra monitoring the photolysis of donor 24a. Additionally, if a stepwise elimination was operating, the rate of decomposition for donor 24a should be similar to, or slower than, that of 24d. However, under identical conditions the rate of decomposition of

24d was approximately three-fold slower than that of 24a (24d t1/2 = 11.0 minutes; 24a t1/2

= 4.0 minutes).47 This disparity in decomposition rates provided further support for the concerted photodecomposition mechanism of 24a outlined in Figure 1.21.

- The production of HNO was initially inferred by NMR detection of CF3SO2 and diol 27. To unambiguously confirm the production of HNO from photoirradiation of donor

+ 24a, aquacobalamin (H2OCb1(III) ) was used as an HNO trapping agent. Previous

+ experiments had determined that H2OCb1(III) reacts stiochiometrically with HNO to

produce nitroxylcobalamin (NO--Cb1(III)).48 Both of these cobalt species are photostable and unreactive with respect to donor 24a. As previously mentioned, cobalt(III) centers are selective to reaction with HNO and no reaction is observed with NO. The conversion of

+ - H2OCb1(III) to NO -Cb1(III) during the photolysis of donor 24a was monitored by UV-

Vis spectroscopy, with clean isosbestic points observed at 367 and 493 nm confirming this reaction (Figure 1.23).46

+ 46 Figure 1.23: UV-Vis spectra showing the reaction of HNO with H2OCb1(III)

Donor 24b decomposed on much slower time scale (t1/2 = 6.3 minutes) than 24a and

- only gave a marginal amount of HNO release (inferred by formation of CH3SO2 : 9% determined by 1H NMR). Donor 24b experienced a much higher percentage of photoredox

N-O bond cleavage (CH3SO2NH2: 77%) in addition to formation of another elimination byproduct (CH3SO2NHOH: 14%). Similarly disappointing results were observed in the photochemical analysis of donor 24c.

1.5.3 Strategies for the Improvement of First-Generation Donor 24a

Donor 24a demonstrated that the 3,2-HNM protecting group is well-suited for the design of a rapid, photo-controlled HNO donor but experienced a competing photoredox

side reaction which limited its utility. Because the proposed mechanism for the photoredox side reaction is dependent upon benzylic proton elimination, we reasoned that structural modifications at the benzylic carbon might influence the selectivity of the photolysis mechanism. We postulated that incorporation of an R group at the benzylic carbon may either inhibit or impede the photoredox reaction in addition to stabilizing the naphthoquinone methide product formed in the HNO-generating pathway (Figure 1.24).

Understanding the impact of this structural modification would shed light on the mechanism of the competing photoredox side reaction and may also offer insight into how this process might be suppressed.

Figure 1.24: Incorporation of a benzylic substituent as a potential strategy to

probe selectivity for HNO generation

A previous member of the Sampson/Seed/Brasch group began investigations into the synthesis of a mono-methyl substituted analog of donor 24a (36, see Figure 1.25).49 A synthetic scheme designed for the preparation of this donor is outlined in Figure 1.25.

Figure 1.25: Synthetic scheme for the preparation of donor 36

Following triisopropylsilylation of the commercially available naphthol 17, reduction of the protected ester (18) was efficiently achieved using a novel combination of reagents. Previous reduction of ester 18 with lithium aluminum hydride produced a deprotected diol as the major product and a small percentage of the desired alcohol (19)

(Figure 1.19). Presumably, the deprotection was mediated via intramolecular hydride transfer which occurred after hydride delivery at the carbonyl carbon (Figure 1.26).49

Figure 1.26: Products of the LiAlH4 reduction of ester 18

In contrast, sodium borohydride reduction was efficiently achieved in the presence

49, 50 of hafnium tetrachloride. In solution, HfCl4 and NaBH4 combine to form a more reactive reducing species, Hf(BH4)4. Additionally, the Lewis acidic hafnium center may complex to the carbonyl oxygen, increasing the electrophilicity of the ester carbonyl carbon. Optimization of these reaction conditions resulted in a four-fold increase in the yield of alcohol 19 compared to previous methods. Facile oxidation to aldehyde 31 was achieved with 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one (Dess-Martin periodinane: DMP). The key benzylic methyl substituent was incorporated via a Grignard reaction, producing secondary alcohol 32. This alcohol was converted to key intermediate

33 via a Mitsunobu reaction utilizing N-hydroxyphthalimide (NHP) as the nucleophilic

species. However, this step proceeded in very low yield and no time was available for further optimization of this chemistry. Preliminary attempts were made to convert intermediate 33 to the target donor 36, but the final product was not successfully isolated.

As a result, optimization of several steps of this synthesis was needed in order to secure a reliable preparation of target donor 36.

1.6 Thesis Project Goals

One of the major goals of this project was to complete the development of a synthetic approach to the target 36, specifically targeting the low-yielding Mitsunobu reaction (32 → 33) for detailed exploration. After completing the optimized synthesis of

36, this donor would be employed to probe the impact of the benzylic methyl substituent on the competing photochemical reactions leading to either HNO generation or photoredox

N-O bond cleavage. Following the results of these photochemical studies, additional analogs could be synthesized using other R groups to probe their HNO donating abilities.

CHAPTER 2. RESULTS AND EXPERIMENTAL DISCUSSION

2.1 Primary Objectives

At the onset of this project we desired to reproduce the initial four steps of the proposed synthesis of donor 36 (Figure 1.25). After successfully preparing secondary alcohol 32, we would begin a detailed study of the optimization of the Mitsunobu reaction

(32 → 33). After obtaining satisfactory results for the Mitsunobu reaction, we would complete the synthesis of donor 36. After completing this synthesis, we planned to perform photochemistry experiments with donor 36 to probe the effect of the added methyl group on the rate and selectivity of the competing pathways in the photolysis reaction observed with donor 24a (Figure 1.21).

2.2 Synthesis of Secondary Alcohol Intermediate 32

The first four steps of the original synthesis leading to alcohol 32 were optimized and improved yields were obtained for several steps (Figure 2.1). No erosion of yield was observed when changing the solvent used for the base-mediated, TIPS protection from dimethylformamide (DMF) to dichloromethane (DCM). Reactions performed in DMF require a more tedious extraction due the amphiphilic nature and high boiling point of this solvent. Thus, the change to DCM simplified the reaction work-up. Following the previous procedure, a solution of the TIPS protected ester (18) was added to a sodium borohydride

hafnium tetrachloride suspension in THF. Following chromatographic purification, alcohol

19 was obtained with improvement of the previous yields. Oxidation of 19 with Dess-

Martin periodinane (DMP) provided the desired aldehyde (31) in quantitative yield. The subsequent Grignard reaction allowed for the insertion of the methyl substituent at the benzylic carbon. Exposure to methylmagnesium bromide under an inert atmosphere and at low temperature (3-5°C) converted aldehyde 31 to secondary alcohol 32 in high yield. The conversion of commercially available methyl 3-hydroxy-2-napthanoate (17) to secondary alcohol 32 was achieved on a 2.5 gram scale with an efficient, four-step, overall yield of

64%.

Figure 2.1: Preliminary steps in the synthesis of donor 36

2.3 Exploration of the Mitsunobu Reaction

2.3.1 Initial Optimization of the Mitsunobu Reaction of Alcohol 32

As previously stated, the conversion of secondary alcohol 32 to adduct 33 via a

Mitsunobu reaction had only proceeded in low yield to date. We desired to invest in the optimization of this reaction for two reasons. First, this reaction occurs at a mid-point stage of the synthesis, making this conversion critical for the overall efficiency of the synthesis.

Also, this reaction is utilized in the synthesis of other analogous donors prepared by our

group. Optimized conditions for this reaction would therefore be valuable for future explorations of this family of HNO donors.

Our first modification to the Mitsunobu reaction procedure involved the solvent.

Previous reactions were performed in DCM, however, we reasoned that the reactants and reagents would have better solubility and reactivity in tetrahydrofuran (THF).

In a detailed study of solvent polarity in the Mitsunobu reaction, Jenkins and coworkers concluded that Mitsunobu reactions performed in THF were superior to more polar solvents.51 Indeed an inverse linear relationship was observed between solvent polarity and rate of Mitsunobu esterification. This result was rationalized by the Hughes-

Ingold rules which state that increased solvent polarity leads to a decrease in rate due to charge stabilization of activated complexes.52 Balancing both reagent solubility and reaction rate, THF was considered to be most efficacious solvent for our reaction.

The Mitsunobu reaction in THF with a slight excess of NHP provided the desired product with a two-fold increase in yield (Table 2.1, entry 2). Extended reaction times

(Table 2.1, entry 3) did not result in a significant increase in yield. Crude 1H NMR analysis revealed that not all starting material (32) had been consumed after ~72 hours at room temperature.

Given that the previous reaction was incomplete even after an extended reaction time, we decided to perform the reaction at elevated temperatures with an excess of each reagent (Table 2.1, entry 4). Unfortunately, this resulted in a lower isolated yield of product 33.

Table 2.1: Preliminary trials of various conditions for the Mitsunobu Reaction

Temp Entry NHP DIAD PPh3 Solvent Time Yield (˚C) 24 1 1.0 eq 1.1 eq 1.1 eq DCM 0 → r.t. 15% hours 24 2 1.4 eq 1.1 eq 1.1 eq THF 0 → r.t. 35% hours 72 3 1.0 eq 1.1 eq 1.1 eq THF r.t. 31% hours 24 4 2.0 eq 2.18 eq 2.0 eq THF 0 → 50 17% hours

One major difficulty associated with the Mitsunobu reaction is the purification of the crude product. After quenching the reaction and extracting the organic products, TLC analysis of the residue shows 5-6 different chromophores with very similar Rf values, complicating the chromatographic separation of the desired product. After purification via flash column chromatography, the product (33) was obtained with impurities and further recrystallization was required to afford the pure product.

In an attempt avoid this complication, an acid-catalyzed substitution reaction was attempted using NHP with para-toluenesulfonic acid (Figure 2.2). Unfortunately, virtually no starting material was consumed during the reaction. It was assumed that the nucleophilicity of NHP is greatly reduced under acidic conditions, making the substitution reaction too slow to be useful.

Figure 2.2: Attempted acid-catalyzed substitution of 32

2.3.2 Mitsunobu Reaction with a 2,6-disubstituted Analog of 32

Revisiting the Mitsunobu reaction, literature precedents showed that Mitsunobu reactions with sterically crowded alcohol centers proved to be consistently low-yielding.

For instance, reaction of the sterically crowded alcohol group in (-)-menthol with benzoic acid under Mitsunobu conditions provided the desired ester in only 20% yield (Figure

2.3).53

Figure 2.3: Mitsunobu reaction of (-)-menthol with benzoic acid 53

We suspected that the triisopropylsilyl protecting group, proximal to the secondary alcohol carbon in 32, provided a substantial amount of steric hindrance which impeded the

Mitsunobu reaction. To provide evidence for this hypothesis, we desired to produce the

2,6-substituted analog of alcohol 32. This analog (41) would provide little to no steric hindrance in the Mitsunobu reaction and would allow us to determine the effect of the proximity of the TIPS group to the alcohol center on the Mitsunobu reaction.

The commercially available methyl 6-hydroxy-2-naphthanoate (37) was converted to the secondary alcohol (41) via a similar sequence employed for the 2,3-disubstituted alcohol (Figure 2.4). Improved yields for the TIPS protection were obtained for the 2,6- disubstitued analog. This can be rationalized by taking into account the substantial difference in steric hindrance between the 2,3 and 2,6-disubstituted naphthols (17 and 37 respectively). Similar yields were obtained for the reduction, oxidation and Grignard steps.

A Mitsunobu reaction of secondary alcohol 41 under identical conditions used with 2,3- alcohol 32 (seen in Table 2.1, entry 3) provided adduct 42 in 92% yield. This result confirmed our assumption regarding the impact of the steric effect of the proximate TIPS group and the yields of the Mitsunobu reaction with the 2,3-disubstituted analog.

Figure 2.4: Synthetic preparation of 2,6-disubstituted analogs

2.3.3 Alternative Methods: Oxazridine Amination

Our previous work had established that conversion of secondary alcohol 32 to adduct 33 via Mitsunobu reaction proved very challenging due to the steric effect of the proximal TIPS group. With this information in hand, we desired to explore an alternative

route to produce the key alkoxyamine intermediate 34. After consulting the literature, an interesting method was found for the direct amination of alcohols. Oxaziridines (43) are heterocyclic compounds that contain oxygen, nitrogen and carbon in a three-membered ring and have been utilized as electrophilic reagents for nitrogen transfer. Oxaziridines have been used to produce amines, amides, hydroxylamines and hydrazines.54 Because of the strained three-membered ring, the N-O bond of oxaziridines is particularly weak and nucleophilic ring-opening occurs most often at the nitrogen atom. The proposed mechanism for the formation of an alkoxyamine from the corresponding alcohol and oxaziridine is shown in Figure 2.5. Under basic conditions, the alcohol attacks the electrophilic nitrogen, breaking open the three-membered ring. Presumably, this initial step would occur very rapidly due to the thermodynamically favorable opening of the strained three-membered ring and cleavage of the weak N-O bond. Consequently, the alcohol may attack in either the protonated or deprotonated state. The resulting intermediate would then collapse, eliminating a ketone and corresponding alkoxyamine after protonation of the nitrogen.

Figure 2.5: Proposed mechanism of alcohol amination via oxaziridine

Although it is most common for the nitrogen of the oxaziridine to be substituted with a non-hydrogen R group, there are a few literature reports which utilize an oxaziridine with a secondary nitrogen. Ellman and coworkers reported the synthesis of an oxaziridine

suitable for the conversion of alcohols to primary alkoxyamines.55 Initially, a cyclohexane derivative (47) was prepared; however, instability and problematic condensation reactions with the desired amine products prevented the application of this compound. Instead they focused on the novel 3,3’-di-tert-butyl oxaziridine analog (49). They reasoned that the tert- butyl groups would provide sufficient steric hindrance to impede condensation side reactions. The oxaziridine was prepared from the corresponding imine (48) via oxidation with 3-chloroperoxybenzoic acid (mCPBA). Bulb-to-bulb distillation was used to separate the oxaziridine from a ketone byproduct. This oxaziridine was then used in the amination of several potassium alkoxides (generated in situ) with good yields of the alkoxyamines

(Figure 2.6). A crown ether was used as a reaction additive which increases the nucleophilicity of the alkoxide by sequestering the potassium cations. Ellman’s oxaziridine has been used successfully by other groups for alcohol amination.51

Figure 2.6: Preparation and application of Ellman’s oxaziridine. 55

We perceived that this oxaziridine chemistry could be applied to our synthesis.

Reaction of secondary alcohol 32 with oxaziridine 49 directly should produce the desired alkoxyamine intermediate (34). Not only would this provide an alternative to the

troublesome Mitsunobu reaction but would also achieve two steps of the original synthesis in one conversion. In our hands, oxidation of the commercially available 3,3’-di-tert-butyl imine (48) produced oxaziridine 49; however, purification of the product proved difficult.

Analyzing the crude 1H NMR spectrum, we found that only two products were present: the desired oxaziridine 49 and 3,3’-di-tert-butyl ketone in an approximately 2:1 ratio.

Assuming that this ketone would not interfere with the amination reaction, we decided to use this impure sample of oxaziridine as a solution in DCM. Generation of the potassium alkoxide of alcohol 32 was achieved with potassium hydride in DMPU (1,3-dimethyl-

3,4,5,6-tetrahydro-2(1H)-pyrimidinone). A solution of oxaziridine 49 and 18-crown-6 was added to a cooled solution of the alkoxide. Two hours after the addition, the reaction was quenched and extracted. Unfortunately, 1H NMR analysis revealed that the alcohol had lost the TIPS protecting group and no appreciable amount of the anticipated alkoxyamine product 34 was formed. Therefore this approach was abandoned and the Mitsunobu conversion of 32 to 33 was revisited.

2.3.4 Literature Regarding Mitsunobu Reactions of Sterically Hindered Alcohols

Given the difficulty involved with the preparation and purification of oxaziridine

49, we elected to revisit the Mitsunobu reaction. Upon further literature exploration, we found several reports discussing modifications that can be made to Mitsunobu reactions involving sterically hindered alcohols. Dodge and coworkers describe the reaction of (-)- menthol with various benzoic acids under Mitsunobu conditions.53 Reaction of benzoic acid with (-)-menthol, triphenylphosphine and diisopropyl azodicarboxylate only provided low yields (20%) of the desired product due to the steric hindrance provided by the

proximal isopropyl group. Interestingly, application of benzoic acids with electron- withdrawing groups (EWG) on the aromatic ring significantly improved the yield of this conversion. For example, use of 4-nitrobenzoic acid and 4-cyanobenzoic acid resulted in a three to four-fold increase in yield of the desired ester (83 and 60% yields, respectively, see Table 2.2). They reasoned that the increased acidity of the EWG-substituted nucleophiles was the source of the improved yields. From this assumption, the authors set out to determine if a correlation existed between nucleophile acidity and efficacy of the

Mitsunobu esterification reaction. Indeed, such a trend was realized; systematic application of a variety of benzoic acid derivatives revealed a direct relation between pKa of the nucleophile and yield of the desired product (Table 2.2). More acidic nucleophiles

(corresponding to lower pKa values) such as 4-nitro-, 4-cyano- and 4- methanesulfonylbenzoic acid provided improved yields when compared to benzoic acid.

Conversely, carboxylic acids with electron donating groups (EDG) such as 4-methyl-, and

4-methoxybenzoic acid possessed higher pKa values and resulted in low yields of the corresponding esters.

Table 2.2: Mitsunobu reaction of (-)-menthol with various benzoic acids 53

Carboxylic Acid pKa (in Ph-CH3) Yield (%)

4-NO2C6H4CO2H 3.41 83

4-NCC6H4CO2H 3.55 60

4-MeSO2C6H4CO2H 3.64 61

4-ClC6H4CO2H 3.98 54

C6H5CO2H 4.19 20

4-CH3C6H4CO2H 4.36 26

4-CH3OC6H4CO2H 4.47 19

In addition to Dodge’s report, a similar study was conducted by Bessodes et al. regarding the use of acetic acid derivatives as nucleophiles in Mitsunobu reactions.57 Five different sterically hindered alcohols were chosen which had previously produced poor yields of the desired ester with benzoic acid. For example substrate 50, which possesses two acetal protecting groups proximal to the alcohol, had been previously reported to produce none of the desired ester in the presence of acetic acid under Mitsunobu conditions.

In contrast, the Mitsunobu esterification with monochloroacetic acid showed good yields for the all inverted alcohols. Once again, the increased yields of these reactions can be attributed to the increased acidity of the chloroacetic acid (pKa = 2.86) compared to acetic acid (pKa = 4.76).

Figure 2.7: Mitsunobu esterification of sterically hindered alcohols with chloroacetic

acid

Rationale for these observations can be found in a detailed, mechanistic study of the Mitsunobu reaction conducted by Hughes and Grabowski.58 Hughes and coworkers divided the mechanism into three discrete steps: adduct formation, alcohol activation, and

SN2 inversion (Figure 2.8).

Figure 2.8: Mechanism of the Mitsunobu Esterification 53

In the first step (Figure 2.8, Step 1) the azodicarboxylate species (e.g. DIAD, 52) is subject to nucleophilic attack at a nitrogen atom by the phosphine species (e.g. PPh3, 51).

This PPh3-DIAD adduct then deprotonates the carboxylic acid to form a positively charged intermediate (53). Hughes performed control experiments to probe the effect of the carboxylic acid on this initial step. When the amount of carboxylic acid is doubled (2 equivalents), the carboxylate reactivity is significantly diminished and thus the positively

charged DIAD-PPh3 intermediate is quite stable (t1/2 = ~15 hours at 30 °C). Hughes attributes this decrease in reactivity to the strong hydrogen bonding between the carboxylic acid and the conjugate carboxylate which decreases the carboxylate nucleophilicity.58

In the following step, an acid/base reaction occurs between carboxylate and alcohol

(Figure 2.8, Step 2). The triphenylphosphine moiety is then transferred to the alkoxide species (55), forming the key oxyphosphonium intermediate (56). The anionic DIAD intermediate is readily protonated by the carboxylic acid, forming the DIAD hydrazide (57) and another equivalent of carboxylate. The rate of triphenylphosphine transfer is dependent on several factors. In addition to alkoxide nucleophilicity, carboxylate basicity and the ratio of carboxylic acid to conjugate base have a significant impact on the rate of alcohol activation/triphenylphosphine transfer. To quantify these factors, a model alcohol was reacted with DIAD and PPh3 in the presence of formic acid. When the ratio of formic acid/formate anion was increased from 0.54 to 2.0, the rate of alcohol deprotonation was decreased 170-fold. The diminished rate is the result of formate anion solvation via hydrogen bonding with the carboxylic acid, effectively negating the carboxylate basicity.

Rates of the oxyphosphonium formation were measured with other carboxylic acids to

determine the effect of basicity on the rate of alcohol activation. As expected, more acidic compounds were much slower to deprotonate the alcohol due to their weak conjugate basicity.

The final step in the Mitsunobu reaction is the SN2 reaction (Figure 2.8, Step 3) in which the carboxylate anion (54) acts as a nucleophile to attack the oxyphosphonium intermediate (56), yielding the desired ester (58) and triphenylphosphine oxide (59). As in previous steps, the ratio of carboxylic acid to carboxylate also affects the rate of the SN2 reaction. Increased concentration of the carboxylic acid slowed this step, again, attributing this decreased rate to hydrogen bond complexation with the carboxylate. The SN2 inversion showed first-order kinetics in alcohol and zero-order kinetics in formate concentration, which is unusual for SN2 reactions. This result can be rationalized by either a salt effect or

51 the aggregation of ion pair clusters. Another factor impacting the efficacy of the SN2 reaction is the carboxylate basicity/nucleophilicity. A Brønsted plot of log k vs pKa (Figure

2.9) shows that there is a less significant dependence on carboxylate basicity for the SN2 reaction compared to the previous alcohol activation step.

Figure 2.9: Brønsted plot of log k vs pKa illustrating the rates of alcohol activation

58 and SN2 reaction with various carboxylic acids (reproduced from Hughes et al.)

One interesting side reaction was recognized in this report. To form the desired ester, intermediate 53 would normally react with the activated alcohol 55. However, when the reaction is carried out in the absence of an alcohol, a side reaction occurs (Figure 2.10).

The carboxylate anion (54) attacks the phosphorus of the DIAD-PPh3 intermediate (53), transferring the triphenylphosphine moiety. Subsequent attack of the anionic azo nitrogen of 61 at the electrophilic carbonyl of intermediate 60 results in an N-acetylated DIAD derivative and triphenylphosphine oxide (Figure 2.10). This control experiment revealed a prevalent, competing pathway in Mitsunobu esterification reactions.

Figure 2.10: Side reaction that occurs when the alcohol is omitted from the

Mitsunobu reaction 58

A complementary report by Hughes gives a highly detailed study of the initial steps

59 of the Mitsunobu esterification. To determine the fate of DIAD/PPh3 intermediate (53) in the presence of different carboxylic acids, reactions were performed in the absence of an alcohol. Three different products were isolated from these reactions: the mono (57a) and bis N-acetylhydrazine (57b) as well as the hydrazide (57). Acetic acid and benzoic acid, along with their more acidic counterparts, chloroacetic and 4-nitrobenzoic acid, were individually reacted with DIAD and PPh3. The data summarized in Table 2.3 shows the ratio of the products for each acid in THF.

Table 2.3: Ratio of products in the alcohol-free Mitsunobu reaction 54

R Group Time

CH3 1 hour 37% 48% 7%

CH2Cl 72 hours 68% 17% 5%

C6H6 2 hours 33% 50% 12%

4-NO2C6H6 48 hours 38% 36% 19%

This summary shows that the decomposition the DIAD-PPh3 intermediate is much slower in stronger acids (chloroacetic acid and 4-nitrobenzoic acid) due to their decreased nucleophilicity. Unfortunately, the activation of the alcohol occurs at a much slower rate with these stronger acids, as previously reported. The overall effect of the stronger acid is a decreased rate of DIAD-PPh3 decomposition to yield a cleaner esterification over a longer reaction time. Hughes concluded this report by stating that there is a “delicate balance” between the acidity and nucleophilicity of the carboxylic acid in these Mitsunobu reactions.

2.3.5 Detailed Exploration of the Mitsunobu Reaction

Based on these reports, we hypothesized that the Mitsunobu reaction of sterically hindered alcohol 32 experienced similar difficulties. We reasoned that the bulk of the proximal TIPS group hindered the triphenylphosphine transfer that occurs in step two as well as the final SN2 inversion. Drawing an analogy with Hughes’ report, it seemed logical that a more acidic NHP nucleophile would hamper any decomposition of the DIAD-PPh3 intermediate and increase the rate of alcohol activation. Thus, we set out to synthesize NHP analogs substituted with electron-withdrawing groups on the aromatic ring. The electron- withdrawing groups would increase the parent acidity by stabilizing the conjugate base as well as decreasing its nucleophilicity. We initially decided to explore chloro- and nitro-

NHP derivatives.

Following a literature precedent, we attempted to prepare the NHP derivatives from the corresponding phthalic anhydrides.60 Under basic conditions, the anhydride (62) would

presumably undergo an initial substitution with the nucleophilic hydroxylamine, followed by subsequent ring closure yielding the N-hydroxyphthalamide (63).

Figure 2.11: Preparation of phthalimides from the corresponding anhydride via

base-mediated hydroxylamine substitution 60

Unfortunately, we did not find this chemistry to be effective. After screening a variety of organic bases (pyridine, triethylamine, N,N-diisopropylamine and 1,8- diazabicyclo[5.4.0]undec-7-ene) even at extended reaction times (>48 hrs) at reflux temperature, we found that no desired product was formed in the reaction. After acidic aqueous workup, the only product recovered was the phthalic acid. This unsuccessful result is likely due to the fact that the ring-closing step of this reaction involves a weak amide nucleophile and a highly ineffective leaving group at the poorly electrophilic carboxylate moiety in the ring-opened intermediate.

Another precedent for the preparation of substituted NHPs was found which involved a multi-step, one-pot reaction.61 Beginning with a phthalimide (64), exposure to di-tert-butyl dicarbonate produces a Boc-protected phthalimide (65) which then readily undergoes transamidation with aqueous hydroxylamine. The resulting ionic salt (66) then yields an NHP (67) upon acidic workup (Figure 2.12).

Figure 2.12: Scheme for one-pot preparation of NHP’s from corresponding

phthalimides 61

Conversion of the commercially available 4-nitrophthalimide (64a) and 4,5- dichlorophthalimide (64b) to their corresponding NHPs (67a-b) preceded smoothly. Both phthalimides readily underwent Boc-protection in the presence of catalytic 4- dimethylaminopyridine (DMAP) with complete conversion occurring within 30 minutes.

Precipitation was observed almost immediately after addition of aqueous hydroxylamine.

This precipitate was easily isolated by filtration after addition of diethyl ether. Following acidic workup with aqueous hydrochloric acid, the solid NHPs were obtained with no further purification required. Though this chemistry was effective, in our hands, these reactions proceeded with noticeably lower isolated yield (57-74%) than those reported in the literature (>95%).61

In addition to the alternative NHP nucleophiles, we prepared other secondary alcohol substrates with various naphthol protecting groups. We desired to explore the relationship between the efficacy of the Mitsunobu reaction and the steric accessibility of the alcohol substrate. We selected an array of protecting groups of varied sizes with the goal of observing a clear trend between reaction yield and steric crowding near the alcohol center. Preparation of MOM (methoxymethyl), SEM (2-(trimethylsilyl)ethoxymethyl),

TBS (tert-butyldimethylsilyl), and PMB (para-methoxybenzyl) protected secondary alcohols (71a-d) followed the synthetic scheme outlined in Figure 2.13.

Figure 2.13: Preparation of secondary alcohols 71a-d with various protecting groups

The protection reactions for both acetal groups (MOM 68a and SEM 68c) were performed with N,N-diisopropylethylamine in DCM, affording good yields of each product after chromatographic purification. The PMB protection (17 → 68b) was carried out with potassium carbonate in DMF at elevated temperatures (65°C). Subsequent purification of the crude material yielded the product (68b) in 87% yield. The moderate yield of the TBS protection (17 → 68d) was due to incomplete consumption of the starting material (17).

This reaction could likely be optimized in the future by extending the reaction time or increasing the temperature. Three of the ester substrates, 68a-c, were then reduced with lithium aluminum hydride, while the HfCl4/NaBH4 protocol was used in the case of the silyl protected analog (68d) due to the anticipated silyl migration observed with LiAlH4 in the TIPS protected analog, 18 (see Figure 1.19). Oxidation of each primary alcohol substrate (69a-d) with DMP followed by Grignard methylation afforded each secondary alcohol target (71a-d) in good, overall yields.

To quantify the steric hindrance associated with each protecting group, Tolman cone angles were calculated for each substrate using computational methods. Tolman cone angles are most commonly used to quantify the steric effects of phosphine ligands on metal complexes. The angle is defined with the vertex at the metal center and most distant atoms on the perimeter of a cone that is defined by the rotational volume of the ligand. Cone angles should be a suitable estimate of steric hindrance for these substrates given that each protecting group experiences free rotation about the oxygen-carbon or oxygen-silicon σ bond. The cone angles were calculated by fitting each protecting group to a palladium(0) center.62 Figure 2.14 depicts the lowest energy conformation structures along with the corresponding Tolman cone angles for each substrate.

Figure 2.14: Calculated cone angles and lowest energy conformation structures for

each secondary alcohol substrate (71a-d)

As expected, the MOM group provided the least hindrance (θ = 121.2°) due to its relatively linear structure and short length. The PMB group is almost entirely planar and can rotate perpendicular to the naphthalene ring, resulting in only marginal steric hindrance. The bulky TBS and TIPS groups have a quaternary silicon atom with alkyl groups projecting out in a tetrahedral array, providing steric bulk at all possible angles.

Interestingly, the SEM group, which is rather linear, has a cone angle similar to the TBS group (θ = 149.3° and 148.8° respectively). This is due to the length of the SEM group (6 atoms linearly) which causes a large rotational cone.

With the NHP derivatives (67a-b) and secondary alcohol substrates (71a-d) in hand, we began to systematically study the Mitsunobu reaction. Optimal reaction conditions were determined by performing reactions with 1.1, 2.0 and 3.0 equivalents of each reagent (NHP, PPh3 and DIAD). No increase in yield was observed when using excess reagents and therefore subsequent reactions were performed with 1.1 equivalent of DIAD and PPh3 and a slight excess of NHP (1.4 equivalents).

Beginning with N-hydroxyphthalimide, a clear relationship between yield and steric accessibility of the alcohol was observed. As anticipated, the yield of each reaction was inversely proportional to the steric bulk of the protecting group (Figure 2.15).

Figure 2.15: Isolated yields of Mistunobu reactions with NHP and alcohol substrates

The protecting groups with the smallest cone angles, MOM (72a) and PMB (72b), both gave similar, high yields of the desired adduct. Notably, the isolated yields of the SEM and TBS analogs (72c and 72d) were identical, demonstrating that the cone angle calculations accurately depicted the steric hindrance provided by the protecting groups in these Mitsunobu reactions.

We then set out to apply our alternative NHP nucleophiles (67a-b) in the Mitsunobu reactions to improve the yields with sterically hindered substrates. To our surprise, erosion of yields was observed with 4-nitro (67a) and 4,5-dichloro NHP (67b) reactions with the secondary MOM-alcohol substrate (68a) (56% and 71% respectively). Even lower conversions were observed when 4-nitro NHP was reacted with the SEM substrate (37%)

(Figure 2.16).

Figure 2.16: Yields for Mitsuobu reactions with EWG-substituted NHPs

We then reasoned that, although these more acidic nucleophiles may have provided rapid alcohol activation (Figure 2.8, Step 2), the electron-withdrawing groups on the aromatic ring significantly decreased the nucleophilicity of the corresponding conjugate bases. The SN2 inversion (Figure 2.8, Step 3) with these more acidic nucleophiles, also likely occurred at a much slower rate compared to N-hydroxyphthalimide, and thus overall provided decreased yields. Indeed, examination of crude 1H NMR spectra revealed that neither of the NHP derivatives (67a-b) were consumed after 24 hours of reaction time.

2.3.6 Synthesis of New NHPs

Given that the addition of electron-withdrawing groups caused a decrease in the

NHP’s nucleophilicity and thus a lower yield in the Mitsunobu reaction, we considered that the addition of electron-donating groups (EDG) might result in the inverse effect. To test

this hypothesis, we set out to synthesize NHP derivatives substituted on the aryl ring with electron-donating groups such as methyl, methoxy and alkylamino. Due to the scarce commercial availability of the requisite phthalimides, we elected to explore new routes to synthesize the requisite NHPs with electron-donating groups. Multiple literature reports were found which described a palladium-catalyzed carbonylation reaction which converted aryl dihalides to phthalimides.63, 64 (Figure 2.17) In this reaction, oxidative addition (A) of an aryl dihalide (76) was followed by insertion of CO (B) into the carbon-palladium bond of intermediate 77. A nitrogenous nucleophile then intercepts this newly formed acyl- palladium species (78) (C) resulting in an aryl halo-amide (79) and a regenerated palladium(0) species. This aromatic halo-amide (79) could then undergo a similar catalytic cycle consisting of oxidative addition (D), carbon monoxide insertion (E) and finally intramolecular nucleophilic substitution (F) to yield the phthalimide (82).

Figure 2.17: General catalytic cycle for palladium-catalyzed carbonylative coupling

leading to phthalimide 82 59

It appeared that this method might be suitable for the preparation of NHPs with electron-donating groups (EDGs). After producing a protected phthalimide, deprotection followed by previously described substitution would yield the desired EDG-substituted

NHPs (Figure 2.18).

Figure 2.18: Proposed method for the preparation of EDG-substituted NHP’s from

aryl dihalides

Literature precedents showed that these carbonylative couplings to produce phthalimides were most effective with aniline motifs.63 However, some benzylamine derivatives had been applied with modest yield.64 Our strategy required the use of a nitrogen nucleophile with a protecting group that could be easily removed prior to hydroxylamine substitution to produce the corresponding NHP. Therefore use of a benzylamine nucleophile could yield the secondary imide after benzyl deprotection.

Previous reports used both aromatic bromides and iodides, with the latter providing better yields of the phthalimides.64, 65 Analogous to a previous report, we elected to use an

N-heterocyclic carbene ligand (85, Figure 2.19) in the reaction. Compared to traditional phosphine ligands, N-heterocyclic carbenes are much stronger σ-donors with virtually no metal-to-ligand π-back bonding, making them ideal for such carbonylation reactions.64

Also, we selected molybdenum hexacarbonyl as a more convenient CO source than gaseous carbon monoxide.63 We initially desired to prepare 4,5-dimethoxy-NHP.

Beginning with commercially available veratrole (83), iodination was easily achieved with iodine and periodic acid (Figure 2.19). After refluxing in methanol for ~5 hours, the diiodinated product 84 was collected via filtration and subsequently recrystallized from methanol. The carbonylation reaction was performed with 4-methoxybenzylamine as the nucleophilic species which effectively served as PMB-protected ammonia.

Figure 2.19: Preparation of PMB-dimethoxy NHP (73) aryl diiodide 72

Only low yields of the PMB-protected phthalimide 86 were isolated after chromatographic purification. In an effort to improve these yields, the corresponding aryl dibromide was prepared. There appeared to be some evidence for protodehalogenation products in 1H NMR analysis of the coupling reaction when using diiodinated product 84.

We postulated that the weak C-I bonds may have been undergone various decomposition reactions, and that the more stable C-Br bonds might provide higher yields of the desired product. After Bromination of 83, aryl dibromide 87 was subjected to identical conditions for the carbonylative coupling reaction. Unfortunately, the aryl bromide provided significantly lower yields of the desired product (86).

Figure 2.20: Preparation of PMB-dimethoxy NHP (73) via aryl dibromide 74

With sufficient quantities of 86 in hand, we desired to carry on to the cleavage of the PMB group from the protected phthalimide (86). Unfortunately, traditional methods of deprotection such acidolysis with trifluoroacetic acid or oxidative methods with 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (DDQ) proved ineffective.66 Efforts are currently underway to optimize this carbonylative-coupling chemistry and develop a method for deprotection of phthalimide 86.

2.6 Synthesis and Analysis of Donor 36

2.6.1 Completion of the Synthesis of Donor 36

We then set out to complete the synthesis of our target donor (36). Given the success that was achieved in the Mitsunobu reaction with the MOM-protected analog, we elected to complete the synthesis of the target with this derivative.

Figure 2.21: Final steps in the synthesis of methanesulfonyl analog of donor 36

The MOM-protected Mitsunobu adduct (72a) was converted to the corresponding alkoxyamine (88) via a Gabriel-type synthesis.

Figure 2.22: Cleavage of the NHP motif to yield alkoxyamine 76

In this reaction, hydrazine cleaves the NHP motif by first breaking one of the imide

C-N bonds. The subsequent intermediate (90) then undergoes ring closure via intramolecular transamidation. The hydrazide byproduct (91) is highly insoluble in DCM and, after filtration, alkoxyamine 88 was obtained in quantitative yield.

Alkoxyamine 88 was then sulfonated with methanesulfonyl chloride, which yielded the SO2CH3 analog of our target donor. Previous studies in our group found that the sulfonylation reaction performed more efficiently with methanesulfonyl chloride compared to trifluoromethanesulfonyl chloride. After determining the best conditions for sulfonylation and MOM deprotection with the SO2CH3 derivative, we planned to apply this chemistry to prepare the SO2CF3 analog (36).

Methanesulfonylation under basic conditions (Figure 2.21, 88 → 89) proceeded in moderate yield (38%) after a tedious chromatographic purification. Unfortunately, attempted deprotection with trimethylsilyl bromide produced many different products.

After analyzing the crude reaction mixture, we were unable to confirm if any of the desired product was produced.

Given the low yield of the sulfonylation reaction with methanesulfonyl chloride, we anticipated (based on prior experience) that application of trifluoromethanesulfonyl chloride under similar conditions would result in even lower yield of desired product (36).

Another common, high-yielding method used for N-sulfonylation involves reaction with the corresponding sulfonic anhydride under basic conditions. We elected to attempt such a reaction with trifluoromethanesulfonic (triflic) anhydride. A solution of alkoxyamine 88 in

DCM with Hünig's base (N,N-diisopropylethylamine) was cooled to -78°C and triflic anhydride was added dropwise. Analysis of the crude reaction mixture showed two major products in an approximately equivalent ratio. To our surprise, chromatographic separation yielded the final target 36 and an N-MOM-protected analog (92).

Figure 2.23: Sulfonation of alkoxyamine 88 with triflic anhydride

To explain this result, we suggest the reaction mechanism outlined in Figure 2.24.

After N-sulfonation of 88, intermediate 93 could then be sulfonated by another equivalent of triflic anhydride at the naphtholic oxygen. With addition of the O-trifyl motif, intermediate 94 has a prime leaving group which could undergo an SN1 cascade elimination. The resulting fragment (95) would be readily scavenged by an equivalent of

N-sulfonated intermediate (93) to yield a bis-MOM protected product (96). This product

(96) could undergo O-MOM deprotection to yield the observed, N-MOM protected product

(92). The bis-sulfonated intermediate 97 could then act as a triflyl source, sulfonating another equivalent of 93 and begin another cycle to produce another equivalent of 94 and target 36.

Figure 2.24: Proposed mechanism for sulfonylation/MOM-deprotection to produce

donor 36

This hypothesis provides a mechanism which is catalytic in the amount of triflic anhydride used for acetal deprotection, accounting for the observed products with the use of only 1.2 equivalents of triflic anhydride. After carefully consulting the literature, we believe that this reaction provides the first example of an acetal deprotection with triflic anhydride. To increase the yield of donor 36 from this reaction, another base could be used which would also serve to scavenge fragment 95, eliminating the production of 92. Efforts are currently underway in the optimization of this chemistry.

2.6.2. Photochemical Analysis of Potential HNO Donor 36

To probe the effect of the added benzylic methyl substituent on the rate and selectivity of photolytic release of HNO from 3,2-HNM-based substrates, donor 36 was subjected to similar photolysis conditions to those employed with donors 24a-c. A sample of donor 36 (~0.5 mg) was prepared anaerobically in a solution of phosphate buffer (0.10 M, pH 7.00) and CD3CN (40:60 v/v, ~1.69 mM) and irradiated in a Rayonet

mini-photoreactor. The progress of the reaction was periodically monitored by 19F NMR spectroscopy. After 15 minutes of irradiation, donor 36 had been completely consumed.

Figure 2.25: 19F NMR analysis of the photodecomposition of donor 36

As anticipated, the photolysis of donor 36 produced two fluorinated species. The peak at -80.34 ppm corresponded to the photoredox sulfonamide byproduct (CF3SO2NH2)

- while the peak at -87.91 ppm corresponded to triflinate (CF3SO2 ) produced during the

HNO generating pathway. We assume that the mechanisms for the two photolysis pathways observed for the decomposition of donor 36 are analogous to those determined for photolysis of the analogous first generation donor 24a (Figure 2.26).

Figure 2.26: Proposed mechanism for photodecomposition of donor 36

Integration ratios show that after 15 minutes of irradiation, donor 36 was

- completely consumed and there was a 28:72 ratio of the CF3SO2NH2/CF3SO2 products.

By comparison with first generation donor 24a, under essentially identical conditions, donor 36 showed approximately a 12% increase in selectivity for the HNO generating pathway (Figure 2.27).

Figure 2.27: Comparison of photolysis product ratio for donor 36 vs. donor 24a

This result supported the aforementioned hypothesis regarding the increased selectivity for HNO generation with a methyl substituted donor. Therefore, we concluded that the incorporation of the methyl group at the benzylic carbon increased the stability of

the intermediate quinone methide (99) giving higher selectivity for the HNO generating pathway (Figure 2.26, Pathway A) during the photolysis reaction.

Further photochemistry experiments will be performed to unambiguously confirm

1 + the generation of products 100, 102 ( H NMR analysis) and HNO (H2OCb1(III) trapping experiments) in addition to determination of the kinetic profile for the photodecomposition of donor 36.

2.7 Future Goals

As we continue this project, one main objective will be to optimize the carbonylative Pd-coupling (84 → 86). This would allow efficient access to a variety of

EDG-substituted NHP’s from their corresponding aryl dihalides. We will then apply each new NHP in Mitsunobu reactions with our series of secondary alcohols (71a-d) with the aim of understanding the relationship among the electronic properties of the NHP nucleophiles, steric hindrance of the protecting group and yield of the Mitsunobu reaction.

We also plan to continue photolytic studies of donor 36 to unambiguously identify all products of its photodecomposition and determine related kinetic data. This study will allow us to confirm that donor 36 undergoes photodecomposition via a mechanism analogous that of the first generation donor 24a.

Finally, we also wish to pursue the synthesis of new 3,2-HNM-based HNO donors.

We hypothesize that incorporation of other benzylic R groups may further improve the selectivity for HNO generation in the photolysis reaction.

Chapter III. Experimental Details

3.1 General Procedures

Unless otherwise noted, all reagents were used as received from the respective supplier (Sigma-Aldrich, Acros Organics, TCI America, Oakwood Chemicals and/or Alfa

Aesar). All anhydrous solvents were distilled under an argon atmosphere. Anhydrous tetrahydrofuran and toluene were distilled from sodium metal/benzophenone. Anhydrous dichloromethane (DCM), 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone (DMPU) and

N,N-diisopropylethylamine (DIPEA) were distilled from CaH2. Commercially available anhydrous N,N-dimethylformamide was used as received. Petroleum ether (bp 66 to 68

°C), ethyl acetate, dichloromethane and diethyl ether used in column chromatography were typically distilled prior to use. Halfnium(IV) chloride was handled inside a glove box under strictly anhydrous conditions (< 5 ppm H2O) due to its highly hygroscopic nature. All structure elucidation was performed using 1H, 13C, and 19F NMR (400, 100 or 376 MHz respectively; Bruker Avance 400 MHz spectrometer running Topspin version 2.1 software). Spectra were referenced either to tetramethylsilane (0.00 ppm), residual chloroform peaks (1H 7.26 ppm, 13C 77.0 ppm), trichlorofluoromethane (19F 0.0 ppm) or

19 13 trifluorotoluene ( F -62.9 ppm in CD3CN). Tentative C NMR signal assignments are labelled with an asterisk (*). 1H NMR signals due to residual solvents are marked with their identity. Reactions were monitored using TLC (aluminum-backed silica gel plates, Sigma-

Aldrich, 200 μm layer thickness, 2-25 μm particle size and 60 Å pore size) or previously

described NMR techniques. Column chromatography was typically performed under positive air pressure (flash column chromatography) using Fisher Scientific silica gel

(SiliaFlash®, 230-400 Mesh).

3.2 Experimental Procedures

Methyl 3-triisopropylsilyloxy-2-naphthanoate (18)

Methyl 3-hydroxy-2-naphthanoate (2.50 g, 12.4 mmol), imidazole (1.35 g, 19.8 mmol) and 4-dimethylaminopyridine (0.151 g, 1.24 mmol) were added to a flask and dissolved in anhydrous DMF (60 mL) under argon. Chlorotriisopropylsilane (3.97 mL,

18.6 mmol, d = 0.901 g/mL at 25°C) was then added dropwise to the flask at room temperature while stirring. The reaction was stirred at room temperature overnight. The reaction was then quenched with brine (60 mL) and extracted with ethyl acetate (2 X 50 mL). The combined organic extracts were washed with brine (75 mL), dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography using a 10:90 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow tinted oil after drying under high vacuum (3.51 g, 79% yield).

1 H NMR (400 MHz, CDCl3) δ 8.24 (s, 1H), 7.80 (dd, J = 8.4, 0.8 Hz, 1H), 7.65 (dd, J =

8.4, 0.8 Hz, 1H), 7.47 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H), 7.34 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H),

7.18 (s, 1H), 3.92 (s, 3H), 1.38 (sept, J = 7.6 Hz, 3H), 1.14 (d, J = 7.6 Hz, 18H).

13 C NMR (100 MHz, CDCl3) δ 167.5, 151.7, 135.8, 132.2, 128.5, 127.9, 127.8, 126.1,

124.5, 124.3, 114.8, 52.1, 17.9 (6C), 13.0 (3C).

[3-(Triisopropylsilyloxy)naphthalen-2-yl]methanol (19)

A flask was charged with halfnium(IV) chloride (1.12 g, 3.50 mmol) and sodium borohydride (0.307 g, 8.12 mmol) under argon, and then cooled in an ice/water bath.

Methyl 3-triisopropylsilyloxy-2-naphthanoate (1.00 g, 2.79 mmol) was added dropwise to the reaction as a solution in anhydrous THF (20 mL) while stirring. The ice bath was then removed and the reaction flask was left to stir overnight at room temperature and then was heated to ~65˚C for an additional 60 minutes. The reaction mixture was then quenched with chilled brine (40 mL) and extracted with EtOAc (15 mL). The aqueous layer was then washed with ethyl acetate (2 x 15 mL). The combined organic extracts were washed successively with saturated aqueous NaHCO3 (15 mL) and brine (15 mL). The organic layer was dried over anhydrous sodium sulfate, filtered, and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 5:95 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow-tinted oil after drying under high vacuum (0.832 g, 90%).

1 H NMR (400 MHz, CDCl3) δ 7.79-7.74 (m, 2H), 7.66 (d, J = 8.0 Hz, 1H), 7.44-7.38 (m,

1H), 7.36-7.30 (m, 1H), 7.14 (s, 1H), 4.87 (d, J = 6.0 Hz, 2H), 2.25 (br t, J = 6.4 Hz, 1H),

1.42 (sept, J = 7.2 Hz, 3H), 1.16 (d, J = 7.2 Hz, 18H).

13 C NMR (100 MHz, CDCl3) δ 152.1, 134.0, 132.6, 128.9, 127.6, 127.3, 126.2, 126.0,

123.9, 112.7, 62.6, 18.1 (6C), 13.0 (3C).

3-(Triisopropylsilyloxy)-2-naphthaldehyde (31)

A flask was charged with Dess-Martin periodinane (1.281 g, 3.020 mmol) flushed under argon and cooled in an ice/water bath. A solution of (3-

(triisopropylsilyloxy)naphthalen-2-yl)methanol (0.832 g, 2.52 mmol) in anhydrous DCM

(30 mL) was added dropwise to the reaction flask. After stirring for 30 minutes the cold bath was removed and the reaction was stirred at room temperature for 90 minutes. The reaction was then quenched with saturated aqueous NaHCO3 (25 mL) and saturated aqueous NaS2O3 (15 mL) and stirred vigorously at room temperature for an additional 10 minutes. The mixture was then extracted with diethyl ether (3 X 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash silica column chromatography using a 5:95 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow amorphous solid after drying under high vacuum (0.820 g, 99%).

1 H NMR (400 MHz, CDCl3) δ ppm 10.67 (s, 1H), 8.37 (s, 1H), 7.88 (dd, J = 8.4, 0.8 Hz,

1H), 7.67 (dd, J = 8.4, 0.8 Hz, 1H), 7.51 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.37 (ddd, J =

8.0, 6.8, 1.2 Hz, 1H), 7.19 (s, 1H), 1.43 (sept, J = 7.6 Hz, 3H), 1.17 (d, J = 7.6 Hz, 18H).

13 C NMR (100 MHz, CDCl3) δ 190.8, 154.5, 137.6, 130.4, 129.9, 128.9, 128.1, 127.3,

126.4, 124.7, 114.3, 18.0 (6C), 13.0 (3C).

1-[3-(triisopropylsilyloxy)naphthalen-2-yl]ethanol (32)

Methylmagnesium bromide (3M in diethyl ether, 5.33 mL, 16.0 mmol) was added dropwise to a cooled solution (~3°C) of 3-(triisopropylsilyloxy)-2-naphthaldehyde (2.10 g,

6.39 mmol) in anhydrous THF (35 mL) while stirring under argon. The cold bath was then removed and the reaction allowed to warm to room temperature and stirred overnight. The reaction mixture was then quenched with saturated aqueous NH4Cl (25 mL) and extracted with diethyl ether (3 X 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered, and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 1:9 ethyl acetate/petroleum ether eluent to afford the title compound as a viscous yellow oil after drying under high vacuum (1.91 g, 87%).

1 H NMR (400 MHz, CDCl3) δ 7.85 (s, 1H), 7.77 (d, J = 8.0 Hz, 1H), 7.64 (d, J = 8.4 Hz,

1H), 7.40 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.32 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.12 (s,

1H), 5.32 (q, J = 6.4 Hz, 1H), 2.50 (br s, 1H), 1.59 (d, J = 6.4 Hz, 3H), 1.43 (sept, J = 7.6

Hz, 3H), 1.16 (d, J =7.6 Hz, 18H).

13 C NMR (100 MHz, CDCl3) δ 151.5, 137.0, 133.6, 128.9, 127.7, 126.1, 125.9, 124.9,

123.8, 112.6, 66.3, 23.2, 18.1 (6C), 13.1 (3C).

N-{1-[3-(Triisopropylsilyloxy)naphthalen-2-yl]ethoxy}isoindoline-1,3-dione (33)

Method 1:

1-(3-((triisopropylsilyl)oxy)naphthalen-2-yl)ethanol (172 mg, 0.499 mmol), N- hydroxyphthalimide (114 mg, 0.699 mmol) and triphenyl phosphine (144 mg, 0.549 mmol) were flushed under argon and dissolved in anhydrous THF (3 mL). After cooling in an ice/water bath to ~3°C, diisopropyl azodicarboxylate (108 µL, 0.549 mmol, d at 25 °C =

1.03 g/cm3) was added dropwise to the reaction. After stirring for 15 minutes, the ice/water bath was removed and the reaction was allowed to warm to room temperature. After stirring overnight, the reaction was quenched with saturated aqueous sodium bicarbonate (10 mL) and extracted with ethyl acetate (2 X 10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 12/88 ethyl acetate/petroleum ether eluent. The obtained solid was then recrystallized from methanol

(2 crops) to afford the title compound as a white crystalline solid after drying under high vacuum (85 mg, 35% yield).

Method 2:

A flask was charged with N-hydroxyphthalimide (0.0473 g, 0.290 mmol) and triphenyl phosphine (0.0837 g, 0.319 mmol). After flushing under argon, 1-(3-

((triisopropylsilyl)oxy)naphthalen-2-yl)ethanol (0.1 M in THF, 2.9 mL, 0.1 g, 0.3 mmol)

was added dropwise as a solution in anhydrous THF (7 mL). Diisopropyl azodicarboxylate

(0.0662 mL, d= 1.027 g/mL at 25˚C, 0.336 mmol) was then added dropwise to the reaction at room temperature. After the stirring at room temperature for 3 days, the reaction mixture was then quenched with brine (10 mL) and extracted with diethyl ether (3 X 10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography with a 1:9 ethyl acetate/petroleum ether eluent. The product was collected along with minor impurities. The crude solid was recrystallized from an ethyl acetate/petroleum ether solution (1:70). The resulting precipitate was then filtered and washed with petroleum ether to afford the title compound as a white crystalline solid after drying under high vacuum (0.045 g, 32%).

1 H NMR (400 MHz, CDCl3) δ 8.33 (s, 1H), 7.89 (dd, J = 8.0, 0.8 Hz, 1H), 7.76-7.70 (m,

2H), 7.69-7.64 (m, 2H), 7.60 (dd, J = 8.0, 0.8, 1H), 7.39 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H),

7.34 (ddd, J = 8.0, 6.8, 1.4 Hz, 1H), 7.05 (s, 1H), 6.17 (q, J = 6.4 Hz, 1H), 1.72 (d, J = 6.4

Hz, 3H), 1.42-1.30 (m, 3H), 1.09 (dd, J = 7.6, 5.6 Hz, 18H).

13 C NMR (100 MHz, CDCl3) δ 163.8 (2C), 151.3, 134.2 (2C)*, 134.0, 132.0, 129.0

(2C)*, 128.7, 128.2, 127.2, 126.3, 126.0, 123.8, 123.3 (2C)*, 112.3, 79.6, 21.3, 18.0 (6C),

13.0 (3C).

Methyl 6-(triisopropylsilyloxy)-2-napthanoate (38)

A round-bottom flask was charged with methyl 6-hydroxy-2-naphthoate (1.50 g,

7.42 mmol), imidazole (0.808 g, 11.9 mmol), and 4-dimethylaminopyridine (0.072 g, 0.59 mmol). After flushing under argon, the solids were dissolved in anhydrous DMF (15 mL) and triisopropylsilyl chloride (2.39 mL, d = 11.2 mmol, 0.901 g/mL at 25°C) was added dropwise while stirring at room temperature. After stirring at room temperature overnight, the reaction mixture was quenched with saturated aqueous sodium bicarbonate (10 mL) and extracted with diethyl ether (2 X 10 mL). The combined organic extracts were washed with brine (30 mL) then dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography with a 5:95 ethyl acetate/petroleum ether eluent to yield the title compound as a yellow tinted oil after drying under high vacuum (2.51 g, 94%).

1 H NMR (400 MHz, CDCl3) δ 8.52 (s, 1H), 8.00 (dd, J = 8.4, 1.6 Hz, 1H), 7.81 (d, J = 8.8

Hz, 1H), 7.69 (d, J = 8.8 Hz, 1H), 7.25-7.20 (m, 1H), 7.16 (dd, J = 8.8, 2.4 Hz, 1H), 3.94

(s, 3H), 1.37-1.26 (m, 3H), 1.12 (d, J = 7.2 Hz, 18H).

[6-(triisopropylsilyloxy)napthalen-2-yl]methanol (39)

A flask was charged with sodium borohydride (0.77 g, 20 mmol) and hafnium(IV) chloride (2.81 g, 8.77 mmol) in an argon atmosphere. The solids were then dissolved in anhydrous THF (10 mL) and the solution was cooled in an ice/water bath (~3°C). A solution of TIPS-protected ester (2.51 g, 7.00 mmol) in THF (10 mL) was added dropwise to the reaction flask while stirring on an ice/water bath (~3°C). After the addition, the ice/water bath was removed and the reaction allowed to warm to room temperature while stirring overnight. The reaction mixture was then quenched with brine (15 mL) and extracted with diethyl ether (3 X 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 10:90 ethyl acetate/petroleum ether eluent to afford the title compound as a dark orange oil after drying under high vacuum (1.96 g, 85%).

1 H NMR (400 MHz, CDCl3) δ 7.68-7.61 (m, 3H), 7.36 (d, J = 8.4 Hz, 1H), 7.22-7.18 (m,

1H), 7.12 (dd, J = 8.8, 2.4 Hz, 1H), 4.71 (s, 2H), 2.27 (br s, 1H), 1.37-1.25 (m, 3H), 1.13

(d, J = 8.0 Hz, 18H).

6-(Triisopropylsilyloxy)-2-naphthaldehyde (40)

A flask was charged with Dess-Martin periodinane (0.677 g, 1.60 mmol), flushed under argon and cooled in an ice/water bath (~3°C). A solution of 6-(triisopropylsilyloxy)-

2-naphthylmethanol (0.440 g, 1.33 mmol) in anhydrous DCM (20 mL) was added dropwise to the stirred reaction. After the addition, the cold bath was removed and the reaction allowed to warm to room temperature. After stirring for 2 hours, the reaction mixture was quenched with saturated aqueous sodium bicarbonate (20 mL) and sodium thiosulfate (1 g) and stirred vigorously. The resulting mixture was then extracted with diethyl ether (3 X

10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent was removed under vacuum. The crude residue was then purified via flash silica column chromatography with a 5:95 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow oil (0.384 g, 88%).

1 H NMR (400 MHz, CDCl3) δ 10.06 (s, 1H), 8.21 (s, 1H), 7.91-7.83 (m, 2H), 7.74 (d, J =

8.8 Hz, 1H), 7.27-7.24 (m, 1H), 7.20 (dd, J = 8.8, 2.4 Hz, 1H), 1.39-1.28 (m, 3H), 1.32

(d, J = 7.2 Hz, 18H).

1-[6-(triisopropylsilyloxy)naphthalen-2-yl]ethanol (41)

Methylmagnesium bromide (970 µL, 2.91 mmol, 3M in Et2O) was added dropwise to a cooled solution (~3°C) of 6-(triisopropylsilyloxy)-2-naphthaldehyde (0.384 g, 1.17 mmol) in anhydrous THF (15 mL) under argon. After stirring for 1 hour, the cold bath was removed and the reaction was allowed to warm to room temperature while stirring overnight. The reaction was quenched with saturated aqueous ammonium chloride (15 mL) and extracted with diethyl ether (3 x 10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography with a 1:9 ethyl acetate/petroleum ether eluent to afford the title compound as a viscous yellow oil after drying under high vacuum (0.358 g, 89%).

1 H NMR (400 MHz, CDCl3) δ 7.78-7.69 (m, 3H), 7.46 (dd, J = 8.4, 1.6 Hz, 1H), 7.29 (d,

J = 2.4 Hz, 1H), 7.20 (dd, J = 9.2, 2.8 Hz, 1H), 5.00 (q, J = 6.4 Hz, 1H), 2.67 (br s, 1H),

1.58 (d, J = 6.4 Hz, 3H), 1.49-1.32 (m, 3H), 1.22 (d, J = 7.2 Hz, 18H).

N-{1-[6-(Triisopropylsilyloxy)naphthalen-2-yl]ethoxy}isoindoline-1,3-dione (42)

A flask was charged with N-hydroxyphthalimide (0.0473 g, 0.290 mmol) and triphenylphosphine (0.0837 g, 0.319 mmol). After flushing under argon, a solution of 1-

(6-((triisopropylsilyl)oxy)naphthalen-2-yl)ethanol (0.10 g, 0.29 mmol) in anhydrous THF

(7 mL) was added to the reaction flask. Diisopropyl azodicarboxylate (66 µL, 0.319 mmol, d = 1.027 g/mL at 25˚C) was added dropwise at room temperature. After stirring at room temperature for 6 days, the reaction mixture was then quenched with brine (10 mL) and extracted with diethyl ether (3 X 10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 7:93 ethyl acetate/petroleum ether eluent to afford the title compound as a white crystalline solid after drying under high vacuum (0.131 g, 92% yield).

1 H NMR (400 MHz, CDCl3) δ 7.77 (s, 1H), 7.75-7.63 (m, 7H), 7.18 (d, J = 2.4 Hz, 1H),

7.09 (dd, J = 8.8, 2.4 Hz, 1H), 5.64 (q, J = 6.4 Hz, 1H), 1.78 (d, J = 6.4 Hz, 3H), 1.35-

1.25 (m, 3H), 1.11 (d, J = 7.2 Hz, 18H).

3,3’-Di-tert-butyloxaziridine (49)

A flask was charged with 2,2,4,4-tetramethyl-3-pentanone imine (0.62 mL, 3.4 mmol, d = 0.809 g/mL at 25°C, 95%) which was then dissolved in anhydrous DCM (5 mL) under argon. The flask was cooled in a brine/ice bath (-1°C). 3-Chloroperoxybenzoic acid

(0.684 g, < 3.05, < 77% mmol) was then added dropwise to the reaction as a solution in anhydrous DCM (3 mL) while stirring. After stirring for 1 hour and 30 minutes the reaction flask was removed from the bath and the solvent removed under vacuum. The reaction mixture was then dissolved in DCM (10 mL) and then washed with saturated aqueous sodium bicarbonate (12 mL) and the organic layer was separated. To quantify the amount of product, benzene (100 μL, 0.876 g/mL at 25°C) was added as an internal standard and

1H NMR spectra were recorded. The product remained in a solution of DCM (0.288 mmol,

8% yield).

*Note: NMR spectra show product before aqueous removal of the mCBA byproduct

1 H NMR (400 MHz, CDCl3) δ 1.27 (18 H).

13 C NMR (100 MHz, CDCl3) δ 85.2, 37.4 (2C), 27.8 (6C).

4-Nitro-N-hydroxyphthalimide (67a)

To a mixture of 4-nitrophthalimide (3.00 g, 15.6 mmol) in anhydrous acetonitrile

(35 mL) was added di-tert-butyl dicarbonate dropwise (3.95 mL, 17.2 mmol, d = 0.95 g/mL at 25°C) under argon. After stirring for 90 minutes, TLC analysis showed that no starting material remained. Aqueous hydroxylamine solution (2.06 mL, 3.6 mmol, 50% w/w, d =

1.078 g/mL at 25°C) was added dropwise to the reaction, which caused the solution to turn bright orange with the formation of a precipitate. After stirring for 3 hours, diethyl ether

(50 mL) was added to the reaction to induce complete precipitation of the product. The orange precipitate was then filtered and washed with water (25 mL) and aqueous HCl (25 mL, 1M) was added to acidify the precipitate. The solution was cooled over 1 hour and the resulting white precipitate was filtered and dried in a vacuum oven (80°C) to afford the title compound as a white solid (1.86 g, 57% yield).

1 H NMR (400 MHz, DMSO-d6) δ 11.19 (s, 1H), 8.62 (dd, J = 8.2, 2.1 Hz, 1H), 8.45 (dd,

J = 2.1, 0.4 Hz, 1H), 8.09 (dd, J = 8.2, 0.4 Hz, 1H).

13 C NMR (100 MHz, DMSO-d6) 162.6, 162.4, 151.4, 133.9, 130.4, 129.7, 124.5, 117.7

4,5-Dichloro-N-hydroxyphthalimide (67b)

To a stirred mixture of 4,5-dichlorophthalimide (1.91 g, 8.84 mmol) in anhydrous acetonitrile (25 mL) was added di-tert-butyl dicarbonate (3.05 mL, 13.3 mmol, d = 0.95 g/mL at 25°C) under argon. After stirring for 3 hours, TLC analysis showed that all starting material had been consumed. Aqueous hydroxylamine solution (1.18 mL, 17.68 mmol,

50% w/w, d = 1.078 g/mL at 25°C) was then added which caused the solution to turn bright orange as a precipitate formed. After stirring overnight diethyl ether (50 mL) was then added to induce complete precipitation. The orange solid was then filtered, suspended in water and aqueous HCl (1M) was added to acidify the solution. The precipitate was collected and dried in a vacuum oven (80°C) to yield the title compound as a white solid

(1.52 g, 74% yield).

1H NMR (400 MHz, DMSO-d6) δ 11.05 (br s, 1H), 8.15 (s, 2H).

13C NMR (100 MHz, DMSO-d6) δ 162.5 (2C), 137.2 (2C), 128.9 (2C), 125.2 (2C).

Methyl 3-(methoxymethoxy)-2-naphthanoate (68a)

Methyl 3-hydroxy-2-naphthanoate (2.00 g, 9.89 mmol) was flushed under argon and dissolved in anhydrous DCM (35 mL). N,N-diisopropylethylamine (5.17 mL, 30.3 mmol, d = 0.757 g/cm3 at 25°C) was then added dropwise to the reaction solution at room temperature while stirring. After stirring for 15 minutes at room temperature, the reaction solution was cooled in an ice/water bath (~2°C) and chloromethyl methyl ether (1.59 mL,

20.9 mmol, d = 1.06 g/mL at 25°C) was added dropwise. After the addition, the ice/water bath was removed and the solution allowed to warm to room temperature while stirring overnight. The reaction was then quenched with brine (40 mL) and extracted with DCM (2

X 35 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a colorless oil after drying under high vacuum (1.99 g, 82% yield).

1 H NMR (400 MHz, CDCl3) δ 8.31 (s, 1H), 7.82 (dd, J = 8.0, 0.4 Hz, 1H), 7.75 (dd, J =

8.0, 0.4 Hz, 1H), 7.55-7.48 (m, 2H), 7.40 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 5.37 (s, 2H),

3.96 (s, 3H), 3.57 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 166.7, 153.0, 135.9, 132.5, 128.6, 128.3, 128.2, 126.8,

124.9, 122.4, 111.4, 95.1, 56.3, 52.3.

[3-(methoxymethoxy)naphthalene-2-yl]methanol (69a)

Lithium aluminum hydride (14.8 mL, 14.8 mmol, 1 M in THF) was added dropwise to a cooled (~3°C) solution of methyl 3-(methoxymethoxy)-2-naphthanoate (3.00 g, 12.2 mmol) in anhydrous THF (50 mL) under an argon atmosphere. After stirring for 60 minutes, the ice/water bath was removed and the reaction was allowed to warm to room temperature while stirring overnight. The reaction was then quenched by the dropwise addition of saturated aqueous ammonium chloride (50 mL). Aqueous hydrochloric acid (50 mL, 1M) was then added to dissolve the solid byproduct. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (2 X 100 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered, and the solvent removed under vacuum to yield a viscous, colorless oil after drying under high vacuum

(2.65 g, > 99% yield).

1 H NMR (400 MHz, CDCl3) δ 7.79-7.71 (m, 3H), 7.47-7.33 (m, 3H), 5.36 (s, 2H), 4.86

(s, 2H), 3.53 (s, 3H) 2.40 (br s, 1H).

13 C NMR (100 MHz, CDCl3) δ 153.2, 133.9, 130.7, 129.2, 127.58, 127.55, 126.8, 126.3,

124.3, 109.0, 94.5, 62.2, 56.3.

3-(methoxymethoxy)naphthalen-2-carbaldehyde (70a)

Dess-Martin periodinane (6.16 g, 14.52 mmol) was flushed under argon, dissolved in anhydrous DCM (20 mL) and cooled in an ice/water bath. A solution of [3-

(methoxymethoxy)naphthalene-2-yl]methanol (2.64 g, 12.10 mmol) in anhydrous DCM

(25 mL) was then added dropwise to the reaction flask while stirring. After stirring for 1 hour, the cold bath was removed and the reaction warmed to room temperature while stirring overnight. The reaction was then quenched with saturated aqueous sodium thiosulfate (15 mL) and saturated aqueous sodium bicarbonate (15 mL) and extracted with

DCM (3 X 30 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow solid after drying under high vacuum (2.27 g, 87% yield).

1 H NMR (400 MHz, CDCl3) δ 10.60 (s, 1H), 8.38 (s, 1H), 7.88 (dd, J = 8.3, 0.3 Hz, 1H),

7.74 (d, J = 8.3 Hz, 1H), 7.53 (ddd, J = 8.2, 6.8, 1.2 Hz, 1H), 7.48 (s, 1H), 7.39 (ddd, J =

8.2, 6.8, 1.2 Hz, 1H), 5.41 (s, 2H), 3.57 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 190.1, 155.0, 137.3, 130.6, 129.8, 129.1, 128.2, 126.9,

125.7, 125.0, 110.1, 94.7, 56.4.

1-[3-(methoxymethoxy)naphthalene-2-yl]ethanol (71a)

Methylmagnesium bromide (9.36 mmol, 3M solution in THF, 3.12 mL) was added dropwise to a cooled (~3°C) solution of 3-(methoxymethoxy)naphthalen-2-carbaldehyde

(0.81 g, 3.75 mmol) in anhydrous THF (15 mL) under argon. The reaction was then removed from the cold bath, allowed to warm to room temperature and stirred overnight.

The reaction was then quenched with saturated aqueous ammonium chloride (20 mL) and extracted with ethyl acetate (3 X 20 mL). The combined organic extracts were then dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a viscous yellow oil after drying under high vacuum (0.85 g, 98% yield).

1 H NMR (400 MHz, CDCl3) δ 7.84 (s, 1H), 7.78 (dd, J = 8.0, 0.6 Hz, 1H), 7.73 (dd, J =

8.0, 0.6, 1H), 7.45-7.39 (m, 2H), 7.36 (ddd, J = 8.0, 6.9, 1.3 Hz, 1H), 5.37 (s, 2H), 5.29-

5.22 (m, 1H), 3.54 (s, 3H), 2.56 (br s, 1H), 1.61 (d, J = 6.5 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 152.6, 135.1, 133.5, 129.2, 127.7, 126.6, 126.2, 125.1,

124.3, 109.0, 94.4, 66.7, 56.3, 23.3.

PMB ester (68b)

Methyl 3-hydroxy-2-napthanoate (2.00 g, 9.89 mmol) and potassium carbonate

(2.73 g, 19.78 mmol) were flushed under argon and suspended anhydrous DMF (40 mL).

4-Methoxybenzyl chloride (2.01 mL, 14.84 mmol, d = 1.155 g/mL at 25°C) was then added dropwise to the solution at room temperature. The reaction was then heated (65°C) and stirred overnight. After cooling to room temperature, the reaction was quenched with brine

(50 mL) and extracted with ethyl acetate (3 X 30 mL). The combined organic extracts were washed with brine (75 mL), dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash silica column chromatography using a 1:4 diethyl ether/petroleum ether eluent to yield the title compound as a white crystalline solid after drying under high vacuum (2.76 g, 87% yield).

1 H NMR (400 MHz, CDCl3) δ 8.33 (s, 1H), 7.82 (dd, J = 8.0, 0.8 Hz, 1H), 7.71 (dd, J =

8.0, 0.8 Hz, 1H), 7.54-7.44 (m, 3H), 7.37 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.27 (s, 1H), 6.96-

6.91 (m, 2H), 5.21 (s, 2H), 3.95 (s, 3H), 3.82 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 166.8, 159.2, 154.7, 136.0, 132.8, 128.8, 128.7, 128.5 (2C),

128.3, 127.6, 126.5, 124.4, 122.2, 113.9 (2C), 108.6, 70.3, 55.3, 52.2.

PMB primary alcohol (69b)

Compound 68b (3.04 g, 9.43 mmol) was flushed under argon, dissolved in anhydrous THF (40 mL) and cooled in an ice/water bath (~3°C). Lithium aluminum hydride (9.83 mL, 23.6 mmol, 2.4 M in THF) was added dropwise to the reaction while stirring on the ice/water bath. The reaction was then removed from the cold bath and allowed to warm to room temperature and stirred overnight. The reaction was then slowly quenched with saturated aqueous ammonium chloride (20 mL) followed by hydrochloric acid (50 mL, 1M) to dissolve the solid byproduct. The mixture was then extracted with ethyl acetate (2 X 30 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed to yield the title compound as an amorphous white solid after drying under high vacuum (2.78 g, > 99% yield).

1 H NMR (400 MHz, CDCl3) δ 7.77 (dd, J = 8.0, 0.8 Hz, 1H), 7.75-7.71 (m, 2H), 7.47-7.33

(m, 4H), 7.32 (s, 1H), 6.98-6.92 (m, 2H), 5.16 (s, 2H), 4.85 (d, J = 6.4 Hz, 2H), 3.83 (s,

3H), 2.41 (br t, J = 6.4 Hz, 1H).

13 C NMR (100 MHz, CDCl3) δ 159.6, 155.1, 134.0, 130.7, 129.1, 128.7, 128.5 (2C), 127.7,

127.5, 126.5, 126.3, 124.0, 114.1 (2C), 106.4, 69.9, 62.6, 55.3.

PMB aldehyde (70b)

Dess-Martin periodinane (4.80 g, 11.3 mmol) was flushed under argon, dissolved in anhydrous DCM (15 mL) and cooled in an ice/water bath (~3 °C). A solution of 69b

(2.78 g, 9.44 mmol) in anhydrous DCM (40 mL) was added dropwise to the reaction while stirring in the ice/water bath. The reaction was then removed from the cold bath and allowed to room temperature while stirring overnight. The reaction was then quenched with saturated aqueous sodium bicarbonate (20 mL) and saturated aqueous sodium thiosulfate

(20 mL) and stirred vigorously. The mixture was then extracted with DCM (2 X 30 mL).

The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then recrystallized from methanol to afford the title compound as a yellow crystalline solid after drying under high vacuum

(1.81 g, 66% yield).

1 H NMR (400 MHz, CDCl3) δ 10.63 (s, 1H), 8.39 (s, 1H), 7.89 (dd, J = 8.0, 0.8 Hz, 1H),

7.73 (dd, J = 8.0, 0.8 Hz, 1H), 7.54 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H), 7.46-7.36 (m, 3H), 7.29

(s, 1H), 6.98-6.94 (m, 2H), 5.21 (s, 2H), 3.84 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 190.26, 159.6, 156.8, 137.5, 132.4, 130.6, 130.0, 129.2

(2C), 128.1, 127.8, 126.7, 125.8, 124.7, 114.1 (2C), 107.7, 70.3, 55.3.

PMB secondary alcohol (71b)

Methylmagnesium bromide (2.07 mL, 6.20 mmol, 3M in Et2O) was added dropwise to a cooled (~3°C) solution of 70b (0.725 g, 2.48 mmol) in anhydrous THF (15 mL) under argon. The reaction was then removed from the ice/water bath and allowed to warm to room temperature while stirring overnight. The reaction was then quenched with saturated aqueous ammonium chloride (25 mL) and the organic layer separated. The aqueous layer was then extracted with diethyl ether (2 X 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum to afford the title compound as a white amorphous solid (0.750 g, 98% yield).

1 H NMR (400 MHz, CDCl3) δ 7.82-7.76 (m, 2H), 7.72 (d, J = 8.0 Hz, 1H), 7.46-7.38 (m,

3H), 7.35 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.24 (s, 1H) 7.00-6.93 (m, 2H), 5.27-5.20 (m,

1H), 5.16 (s, 2H), 3.84 (s, 3H), 2.71 (br d, 4.8 Hz, 1H), 1.60 (d, J = 6.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 159.6, 154.6, 135.0, 133.6, 129.2, 128.8, 128.5 (2C),

127.7, 126.3, 126.2, 125.2, 124.0, 114.1 (2C), 106.6, 69.9, 67.0, 55.3, 23.0.

SEM-ester (68c)

Methyl-3-hydroxy-2-napthanoate (2.00 g, 9.89 mmol) was flushed under argon and dissolved in anhydrous DCM (35 mL). N,N-Diisopropylethylamine (5.17 mL, 30.3 mmol, d = 0.757 g/mL at 25°C) was then added to the reaction solution while stirring at room temperature. After stirring for 15 minutes the reaction solution was cooled in an ice/water bath (~2°C) and 2-(trimethylsilyl)ethoxymethyl chloride (2.10 mL, 11.9 mmol, d = 0.942 g/mL at 25°C) was added dropwise to the reaction mixture. The reaction was removed from the ice/water bath and allowed to warm to room temperature while stirring overnight. TLC analysis of a crude aliquot showed that a significant amount of starting material remained.

Additional N,N-diisopropylethylamine (5.17 mL, 30.3 mmol, d = 0.757 g/mL at 25°C) was then added and the reaction stirred for 3 days. The reaction was then quenched with brine

(50 mL) and the organic layer separated. The aqueous layer was washed with DCM (2 X

35 mL) and the combined organic extracts were washed with HCl (1 M, 40 mL), dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a colorless oil after drying under high vacuum (2.46 g, 75% yield).

1 H NMR (400 MHz, CDCl3) δ 8.29 (s, 1H), 7.82 (dd, J = 7.6, 0.8 Hz, 1H), 7.74 (dd, J =

7.6, 0.8 Hz, 1H), 7.54-7.47 (m, 2H), 7.39 (ddd, J =8.4, 7.2, 1.2 Hz, 1H), 5.41 (s, 2H),

3.95 (s, 3H), 3.87-3.83 (m, 2H), 1.01-0.97 (m, 2H), 0.00 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 166.7, 153.2, 135.9, 132.4, 128.6, 128.2, 128.0, 126.8,

124.7, 122.4, 111.3, 93.6, 66.6, 52.2, 18.1, -1.4 (3C).

SEM primary alcohol (69c)

Compound 68c (2.46 g, 7.40 mmol) was flushed under argon, dissolved in anhydrous THF (30 mL) and cooled (~2°C) in an ice/water bath. Lithium aluminum hydride (14.8 mL, 15 mmol, 1M in THF) was then added dropwise to the reaction while stirring in the cold bath. The reaction was stirred in the ice/water bath for 2 hours, then the bath was removed and the reaction was allowed to warm to room temperature and stirred overnight. The reaction was then slowly quenched with saturated aqueous ammonium chloride (25 mL) and the organic layer separated. The aqueous layer was then washed with ethyl acetate (2 X 50 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography with a 30:70 DCM/petroleum ether eluent. After passing through 500 mL of solvent the eluent was changed to 50:50 DCM/petroleum ether.

After passing through another 500 mL of solvent the eluent was changed to DCM. The pure product was then collected and the solvent removed under vacuum to yield a colorless oil (1.91 g, 85% yield).

1 H NMR (400 MHz, CDCl3) δ 7.80-7.71 (m, 3H), 7.46-7.40 (m, 2H), 7.36 (ddd, J = 8.1,

6.9, 1.3 Hz, 1H), 5.41 (s, 2H), 4.85 (d, J = 6.3 Hz, 2H), 3.84-3.77 (m, 2H), 2.40 (br t, J =

6.3 Hz, 1H), 1.03-0.96 (m, 2H), 0.00 (s, 9H) ppm

13 C NMR (100 MHz, CDCl3) δ 153.5, 134.0, 130.8, 129.1, 127.6, 127.5, 126.7, 126.3,

124.2, 109.1, 93.1, 66.7, 62.4, 18.1, -1.5 (3C).

SEM aldehyde (70c)

To a cooled (2°C) solution of Dess-Martin periodinane (3.19 g, 7.53 mmol) in anhydrous DCM (20 mL) under argon was added a solution of 69c (1.91 g, 6.27 mmol) in

DCM (10 mL) while stirring. The solution was left to stir in the ice/water bath for 1 hour, after which the reaction was allowed to warm to room temperature and stirred overnight.

The reaction was then quenched with saturated aqueous sodium thiosulfate (15 mL) and saturated aqueous sodium bicarbonate (15 mL). The organic layer was separated and the aqueous layer was extracted with DCM (2 X 30 mL). The combined organic extracts were then dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum.

The crude residue was purified via flash silica column chromatography using a 1:1

DCM/petroleum ether eluent to afford the title compound as a yellow solid after drying under high vacuum (1.68 g, 88% yield).

1 H NMR (400 MHz, CDCl3) δ 10.60 (s, 1H), 8.38 (s, 1H), 7.89 (dd, J = 8.2, 0.4 Hz, 1H),

7.75 (d, J = 8.2 Hz, 1H), 7.57-7.50 (m, 2H), 7.40 (ddd, J = 7.8, 7.0, 1.2 Hz, 1H), 5.46 (s,

2H), 3.88-3.82 (m, 2H), 1.04-0.97 (m, 2H), 0.01 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 189.2, 154.3, 136.4, 129.6, 128.8, 128.1, 127.2, 125.9,

124.8, 123.9, 109.1, 92.3, 65.9, 17.1, -2.4 (3C).

SEM secondary alcohol (71c)

Methylmagnesium bromide (4.58 mL, 13.7 mmol, 3.0 M) was added dropwise to a cooled (~3°C) solution of 70c (1.66 g, 5.49 mmol) in anhydrous THF (30 mL) under argon while stirring. After stirring for 1 hour, the reaction was removed from the ice/water bath and allowed to warm to room temperature while stirring overnight. The reaction was then quenched with ammonium chloride (20 mL) and the organic layer separated. The aqueous layer was extracted with ethyl acetate (2 X 30 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed. The crude residue was purified via flash silica column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow oil (1.61 g, 92% yield).

1 H NMR (400 MHz, CDCl3) δ 7.83 (s, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.73 (d, J = 8.1 Hz,

1H), 7.45-7.40 (m, 2H), 7.39-7.33 (m, 1H), 5.41 (s, 2H), 5.25 (m, 1H), 3.84-3.78 (m, 2H),

2.65 (br d, J = 6.5 Hz, 1H), 1.61 (d, J = 6.5 Hz, 3H), 1.03-0.97 (m, 2H), 0.01 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 152.9, 135.1, 133.6, 129.1, 127.7, 126.6, 126.1, 125.0,

124.2, 109.0, 92.9, 66.8, 66.6, 23.3, 18.0, -1.4 (3C).

TBS ester (68d)

Methyl 3-hydroxy-2-napthanoate (2.50 g, 12.4 mmol), imidazole (2.10 g, 30.8 mmol), 4 dimethylaminopyridine (152 mg, 1.24 mmol) and tert-butyldimethylsilyl chloride (2.80 g, 18.6 mmol) were flushed under argon and dissolved in anhydrous DMF.

After stirring overnight a significant amount of starting material remained so additional imidazole (2.10 g, 30.8 mmol) and tert-butyldimethylsilyl chloride (0.93 g, 6.2 mmol) were added and the reaction heated for 4 hours (70-100°C). TLC analysis showed that some starting material still remained. The reaction was then left to stir for two days and afterwards was heated for an additional eight hours (60-70°C). The reaction was then quenched with brine (50 mL) and diluted with ethyl acetate (50 mL). The organic layer was separated and the aqueous layer was extracted with ethyl acetate (2 X 50 mL). The combined organic extracts were dried washed with brine (2 X 75 mL), dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash column chromatography using a 5:95 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow oil after drying under high vacuum

(2.275 g, 58% yield).

1 H NMR (400 MHz, CDCl3) δ 8.28 (s, 1H), 7.81 (dd, J = 8.4, 0.8 Hz, 1H), 7.68 (dd, J =

8.4, 0.8 Hz, 1H), 7.49 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H), 7.36 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H),

7.20 (s, 1H), 3.93 (s, 3H), 1.04 (s, 9H), 0.27 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 167.3, 151.3, 135.9, 132.6, 128.6 (2C)*, 128.1, 126.3, 124.5

(2C)*, 116.0, 52.1, 25.7 (3C), 18.3, -4.4 (2C).

TBS primary alcohol (69d)

A flask was charged with hafnium(IV) chloride (1.00 g, 3.12 mmol) and sodium borohydride (790 mg, 20.9 mmol) under an argon atmosphere. The flask was then placed in an ice/water bath and the solids were suspended in anhydrous THF (20 mL). A solution of 68d (2.27 g, 7.17 mmol) in anhydrous THF (15 mL) was added dropwise to the reaction mixture while stirring on the cold bath. After stirring for 30 minutes, the reaction was removed from the bath and allowed to warm to room temperature. After stirring overnight, the reaction was quenched with saturated aqueous ammonium chloride (20 mL) and the organic layer separated. The aqueous layer was extracted with ethyl acetate (2 X 35 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed. The crude residue was then purified via flash silica column chromatography using a 5:95 ethyl acetate/petroleum ether eluent to afford the title compound as a colorless oil after drying under high vacuum (1.96 g, 95% yield).

1 H NMR (400 MHz, CDCl3) δ 7.79-7.73 (m, 2H), 7.67 (dd, J = 8.0, 0.4 Hz, 1H), 7.41

(ddd, J = 8.4, 7.2, 1.6 Hz, 1H), 7.34 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.14 (s, 1H), 4.82 (s,

2H), 2.29 (br s, 1H), 1.05 (s, 9H), 0.33 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 151.8, 133.9, 132.8, 129.0, 127.6, 127.4, 126.3, 126.1,

124.0, 113.3, 62.4, 25.8 (3C), 18.2, -4.29 (2C).

TBS aldehyde (70d)

Dess-Martin periodinane (3.45 g, 8.13 mmol, 1.2 equiv) was flushed under argon, dissolved in anhydrous DCM (15 mL) and cooled in an ice/water bath (~3°C). A solution of 69d (1.96 g, 6.79 mmol) was in anhydrous DCM (15 mL) was added to the reaction dropwise while stirring. After stirring for 30 minutes the reaction was removed from the bath and allowed warmed to room temperature. After stirring overnight the reaction was quenched with saturated aqueous sodium bicarbonate (15 mL) and saturated aqueous sodium thiosulfate (15 mL). The mixture was extracted with DCM (2 X 25 mL) and the combined organic extracts were dried over anhydrous sodium sulfate and the solvent removed under vacuum. The crude residue was purified via flash silica column chromatography using a 1:1 DCM/petroleum ether eluent to afford the title compound as a bright yellow crystalline solid after drying under high vacuum (1.45 g, 75% yield).

1 H NMR (400 MHz, CDCl3) δ 10.59 (s, 1H), 8.34 (s, 1H) 7.89 (dd, J = 8.4, 0.8 Hz, 1H),

7.70 (dd, J = 8.4, 0.8 Hz, 1H), 7.52 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H), 7.38 (ddd, J = 8.0, 6.8,

1.2 Hz, 1H), 7.19 (s, 1H), 1.06 (s, 9H), 0.34 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 190.6, 154.0, 137.5, 130.5, 129.9, 129.0, 128.2, 127.5,

126.4, 124.8, 115.0, 25.7 (3C), 18.3, -4.3 (2C).

TBS secondary alcohol (71d)

Methylmagnesium bromide (4.20 mL, 12.6 mmol, 3.0 M in Et2O, 2.5 equiv) was added dropwise to a cooled (~3°C) solution of 70d (1.44 g, 5.03 mmol) in anhydrous THF

(25 mL) under argon while stirring. The reaction was then removed from the cold bath and allowed to warm to room temperature. After stirring overnight, the reaction was then quenched with saturated aqueous ammonium chloride (15 mL) and extracted with ethyl acetate (2 X 20 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 12:88 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow tinted oil after drying under high vacuum (1.25 g, 82% yield).

1 H NMR (400 MHz, CDCl3) δ 7.85 (s, 1H), 7.77 (dd, J = 8.0, 0.4 Hz, 1H), 7.66 (dd, J =

8.0, 0.4 Hz, 1H) 7.40 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.33 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H)

7.13 (s, 1H), 5.31-5.23 (m, 1H), 2.40 (br d, J = 4.0 Hz, 1H) 1.58 (d, J = 6.4 Hz, 3H), 1.06

(s, 9H), 0.35 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 151.2, 137.3, 133.5, 129.0, 127.7, 126.1, 126.0, 125.0,

124.0, 113.1, 66.1, 25.8, 23.2 (3C), 18.3, -4.1 (2C).

MOM Mitsunobu (72a)

Compound 71a (233 mg, 1.00 mmol), triphenylphosphine (289 mg, 1.10 mmol) and N-hydroxyphthalamide (180 mg, 1.10 mmol) were flushed under argon, dissolved in anhydrous THF (4 mL) and cooled in an ice/water bath. Diisopropyl azodicarboxylate (216

µL, 1.10 mmol, d = 1.027 g/mL at 25°C) was then added to the reaction while stirring in the ice/water bath. The reaction was then removed from the cold bath and allowed to warm to room temperature and stirred overnight. The reaction was then quenched with saturated aqueous sodium bicarbonate (5 mL) and the organic layer separated. The aqueous layer was then extracted with ethyl acetate (15 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude product was then recrystallized from methanol to afford the title compound as a white crystalline solid after drying under high vacuum (345 mg, 92% yield).

1 H NMR (400 MHz, CDCl3) δ 8.23 (s, 1H), 7.86 (dd, J = 8.0, 0.8 Hz, 1H), 7.78-7.73 (m,

2H), 7.71-7.65 (m, 3H), 7.42 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.39-7.33 (m, 2H), 6.07 (q, J

= 6.4 Hz, 1H), 5.27 (s, 2H), 3.46 (s, 3H), 1.78 (d, J = 6.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 163.9 (2C), 152.7, 134.3 (2C)*, 134.1, 129.7, 129.0 (2C)*,

128.9, 128.1, 127.5, 126.6, 124.3, 123.3 (2C)*, 108.8, 94.5, 79.8, 56.1, 20.5.

PMB-Mitsunobu (72b)

Compound 71b (0.155 g, 0.500 mmol), triphenylphosphine (0.144 g, 0.549 mmol) and N-hydroxyphthalimide (0.115 g, 0.705 mmol) were flushed under argon, dissolved in anhydrous THF (3 mL) and cooled in an ice/water bath (~3 °C). Diisopropyl azodicarboxylate (108 µL, 0.550 mmol, d = 1.027 g/mL at 25°C) was added to the reaction while stirring in the ice/water bath. The reaction was then removed from the cold bath and stirred overnight at room temperature. The reaction was then quenched with saturated aqueous sodium bicarbonate (10 mL) and the organic layer separated. The aqueous layer was then extracted with diethyl ether (10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed. The crude residue was purified via flash silica column chromatography using a 1:1 DCM/petroleum ether eluent and then a DCM eluent to afford the title compound as a crystalline white solid after drying under high vacuum (0.210 g, 93%).

1 H NMR (400 MHz, CDCl3) δ 8.24 (s, 1H), 7.85 (d, J = 7.6 Hz, 1H), 7.73-7.61 (m, 5H),

7.41 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.38-7.29 (m, 3H), 7.15 (s, 1H), 6.90-6.85 (m, 2H),

6.07 (q, J = 6.8 Hz, 1H), 5.10 (d, J = 11.2 Hz, 1H), 5.01 (d, J = 11.2 Hz, 1H) 3.80 (3 H),

1.77 (d, J = 6.8 Hz, 3H).

100

13 C NMR (100 MHz, CDCl3) δ 163.8 (2C), 159.3, 154.2, 134.1 (2C)*, 129.9, 128.9,

128.8 (2C)*, 128.7, 128.5 (2C), 128.2, 127.4 (2C)*, 126.6, 126.3, 123.9, 123.3 (2C)*,

113.9 (2C), 106.4, 79.9, 69.8, 55.2, 20.5.

101

SEM Mitsunobu (72c)

Compound 71c (160 mg, 0.500 mmol), N-hydroxyphthalamide (115 mg, 0.705 mmol) and triphenyl phosphine (144 mg, 0.549 mmol) were flushed under argon, dissolved in anhydrous THF (3 mL) and cooled in an ice/water bath (~3°C). Diisopropyl azodicarboxylate (108 µL, 0.55 mmol, d = 1.027 g/mL at 25°C) was added to the reaction while stirring on the ice/water bath. The reaction was then removed from the cold bath and allowed to warm to room temperature while stirring overnight. The reaction was quenched with saturated aqueous sodium bicarbonate (10 mL) and extracted with ethyl acetate (2 X

10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 12:88 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow oil after drying under high vacuum (0.154 mg, 67% yield).

1 H NMR (400 MHz, CDCl3) δ 8.24 (s, 1H), 7.86 (dd, J = 8.0, 0.8 Hz, 1H), 7.77-7.71 (m,

2H), 7.71-7.65 (m, 3H), 7.44-7.37 (m, 2H), 7.36 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 6.07 (q, J

= 6.8 Hz, 1H), 5.32 (s, 2H), 3.84-3.69 (m, 2H), 1.77 (d, J = 6.8 Hz, 3H), 0.99-0.91 (m, 2H),

-0.02 (s, 9H).

13 C NMR (100 MHz, CDCl3) δ 163.9 (2C), 152.8, 134.2 (2C)*, 134.1, 129.8, 128.92

(2C)*, 128.85, 128.1, 127.3, 126.6, 126.5, 124.1, 123.3 (2C)*, 108.8, 92.9, 79.9, 66.4, 20.6,

18.0, -1.5 (3C).

102

TBS Mitsunobu (72d)

Compound 71d (152 mg, 0.500 mmol), N-hydroxyphthalamide (115 mg, 0.700 mmol) and triphenyl phosphine (144 mg, 0.55 mmol) were flushed under argon and dissolved in anhydrous THF (3 mL). After cooling in an ice/water bath (~3°C) diisopropyl azodicarboxylate (108 µL, 0.549 mmol, d = 1.027 g/mL at 25°C) was added to the reaction while stirring. The reaction was then removed from the ice/water bath and allowed to warm to room temperature. After stirring overnight, the reaction was quenched with saturated aqueous sodium bicarbonate (10 mL) and extracted with ethyl acetate (2 X 10 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was then purified via flash silica column chromatography using a 12:88 ethyl acetate/petroleum ether eluent to afford the title compound as a white amorphous solid after drying under high vacuum (148 mg, 66% yield).

1 H NMR (400 MHz, CDCl3) δ 8.28 (s, 1H), 7.87 (d, J = 8.0 Hz, 1H), 7.78-7.72 (m, 2H),

7.71-7.64 (s, 2H), 7.62 (d, J = 8.0 Hz, 1H), 7.40 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.34

(ddd, J = 8.0 Hz, 6.8, 1.2 Hz, 1H), 7.08 (s, 1H), 6.05 (q, J = 6.4 Hz, 1H), 1.72 (d, J = 6.4

Hz, 3H), 1.02 (s, 9H), 0.30 (s, 3H), 0.26 (s, 3H).

103

13 C NMR (100 MHz, CDCl3) δ 163.9 (2C), 151.1, 134.2 (2C)*, 134.0, 132.1, 129.0,

128.9 (2C)*, 128.2, 127.2, 126.3, 126.1, 123.9, 123.4 (2C)*, 113.0, 79.9, 25.8 (3C), 21.0,

18.3, -4.1, -4.4.

104

MOM Mitsunobu-NO2 (73)

Compound 71a (233 mg, 1.00 mmol), triphenylphosphine (289 mg, 1.10 mmol) and 4-nitro-N-hydroxyphthalimide (229 mg, 1.10 mmol) were flushed under argon, dissolved in anhydrous THF (4 mL) and cooled in an ice/water bath. Diisopropyl azodicarboxylate (216 µL, 1.10 mmol, d = 1.027 g/mL at 25°C) was then added to the reaction while stirring in the ice/water bath. The reaction was then removed from the cold bath and allowed to warm to room temperature and stirred overnight. The reaction was quenched with saturated aqueous sodium bicarbonate (5 mL) and the organic layer separated. The aqueous layer was then extracted with DCM (15 mL) and the combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude product was then recrystallized from methanol to afford the title compound as an orange amorphous solid after drying under high vacuum (235 mg,

56% yield).

1 H NMR (400 MHz, CDCl3) δ 8.57-8.52 (m, 2H), 8.18 (s, 1H), 7.94-7.90 (m, 1H), 7.84

(dd, J = 8.4, 0.8 Hz, 1H), 7.69 (dd, J = 8.4, 0.8 Hz, 1H), 7.46-7.32 (m, 4H), 6.10 (q, J =

6.4, 1H), 5.27 (s, 2H), 3.47 (s, 3H), 1.80 (d, J = 6.4 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 161.7, 161.5, 152.6, 151.6, 134.2, 133.3, 130.1, 129.3,

129.0, 128.8, 128.0, 127.6, 126.8, 126.6, 124.5, 124.4, 118.6, 108.9, 94.6, 80.4, 56.2, 20.3.

105

MOM Mitsunobu-Cl2 (74)

Compound 71a (233 mg, 1.00 mmol), triphenylphosphine (289 mg, 1.10 mmol) and 3,4-dichloro-N-hydroxyphthalamide (255 mg, 1.10 mmol) which was then flushed under argon, dissolved in anhydrous THF (4 mL) and cooled in an ice/water bath.

Diisopropyl azodicarboxylate (216 µL, 1.10 mmol, d = 1.027 g/mL at 25°C) was then added to the reaction while stirring in the ice/water bath. After stirring overnight the reaction was quenched with saturated aqueous sodium bicarbonate (5 mL) which caused the formation of an insoluble byproduct. The organic layer was diluted with DCM (10 mL) and then separated. The aqueous layer was then extracted with DCM (15 mL) and the combined organic extracts were dried over anhydrous sodium sulfate filtered and the solvent removed under vacuum. The crude product was then recrystallized from methanol to afford the title compound as a green crystalline solid after drying under high vacuum

(316 mg, 72% yield).

1 H NMR (400 MHz, CDCl3) δ 8.16 (s, 1H), 7.89-7.77 (m, 3H), 7.67 (d, J = 8.0 Hz, 1H),

7.41 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 7.38-7.31 (m, 2H), 6.05 (q, J = 6.8 Hz, 1H), 5.27 (s,

2H), 3.48 (s, 3H), 1.78 (d, J = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 162.0 (2C), 152.8, 139.2, 134.2 (2C)*, 129.2, 128.9 (2C)*,

128.1, 127.9, 127.6, 126.8, 126.6, 125.5 (2C)*, 124.4, 108.9, 94.6, 80.2, 56.2, 20.4.

106

SEM Mitsunobu-NO2 (75)

Compound 71c (319 mg, 1.00 mmol), triphenylphosphine (289 mg, 1.10 mmol) and 4-nitro-N-hydroxyphthalamide (229 mg, 1.10 mmol) were flushed under argon, dissolved in anhydrous THF (4 mL) and cooled in an ice/water bath. Diisopropyl azodicarboxylate (216 µL, 1.10 mmol, d = 1.027 g/mL at 25°C) was then added to the reaction while stirring in the ice/water bath. After stirring overnight the reaction was quenched with saturated aqueous sodium bicarbonate (5 mL). The organic layer was diluted with DCM (10 mL) and then separated. The aqueous layer was then extracted with

DCM (15 mL) and the combined organic extracts were dried over anhydrous sodium sulfate filtered and the solvent removed under vacuum. The crude product was then recrystallized from methanol. The precipitate was then filtered and purified via flash silica column chromatography using a 15:85 ethyl acetate/petroleum ether eluent to afford the title compound as a viscous yellow oil after drying under high vacuum (173 mg, 37% yield).

1 H NMR (400 MHz, CDCl3) δ 8.57-8.51 (m, 2H), 8.18 (s, 1H), 7.95-7.90 (m, 1H), 7.84 (d,

J = 8.0 Hz, 1H), 7.68 (d, J = 8.0 Hz, 1H), 7.39-7.34 (m, 2H), 7.24 (ddd, J = 8.0, 6.8, 1.2

Hz, 1H), 6.10 (q, J = 6.4 Hz, 1H), 5.33-5.27 (m, 2H), 3.83-3.69 (m, 2H), 1.79 (d, J = 6.4,

3H), 0.99-0.91 (m, 2H), -0.02 (s, 9H).

107

13C NMR 161.7, 161.5, 152.8, 151.8, 134.3, 133.5, 130.4, 129.4, 129.2, 128.8, 128.1,

127.6, 126.8, 126.7, 124.7, 124.4, 118.8, 109.0, 93.1, 80.5, 66.6, 20.5, 18.0, -1.4 (3C).

108

1,2-Diiodo-4,5-dimethoxybenzene (84)

Periodic acid (1.98 g, 8.69 mmol) and iodine (4.41 g, 17.4 mmol) were flushed under argon and dissolved in methanol. 1,2-Dimethoxybenze (2.77 mL, 21.7 mmol, d =

1.084 g/mL at 25°C) was then added dropwise at room temperature. The reaction was then heated to reflux (64-66°C) for 5 hours, after which the heat was removed and the reaction left to stir overnight. The solution was reheated and the solution was filtered hot. The supernatant solution was then quenched with brine (40 mL) and saturated aqueous sodium thiosulfate (15 mL) and extracted with ethyl acetate/DCM (3:2) (2 X 50 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed to an amorphous solid. This solid was then recrystallized from methanol to yield colorless crystals after drying under high vacuum (combined yield of precipitate and recrystallized material: 6.99 g, 82% yield).

1 H NMR (400 MHz, CDCl3) δ 7.24 (s, 2H), 3.84 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 149.5 (2C), 121.6 (2C), 96.0 (2C), 56.1 (2C).

109

PMB-phthalimide (86)

Method 1: 1,2-Diiodo-4,5-dimethoxybenzene (780 mg, 2.00 mmol), molybdenum hexacarbonyl (528 mg, 2.00 mmol), 1,3-bis-(2,6-diisopropylphenyl)imidazolinium chloride (51 mg, 0.12 mmol) and palladium (II) chloride (11 mg, 0.062 mmol) were flushed under argon and dissolved in anhydrous toluene (15 mL). 4-Methoxybenzylamine (314 µL,

(100 mL) and extracted with DCM (3 X 100 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude residue was purified via flash silica column chromatography using a 1:99 methanol/DCM eluent. The pure desired product was collected and the solvent removed to afford the title compounds as a brown solid (161 mg). Some impure fractions were also collected, combined, and the solvent removed. The resulting crude solid was recrystallized

110

from methanol to afford the title compounds as a brown solid after drying under high vacuum (30 mg) (Total: 191 mg, 29% yield).

Method 2: 1,2-Dibromo-4,5-dimethoxybenzene (592 mg, 2.00 mmol), molybdenum hexacarbonyl (528 mg, 2.00 mmol), 1,3-Bis-(2,6-diisopropylphenyl)imidazolinium chloride (51 mg, 0.12 mmol) and palladium (II) chloride (11 mg, 0.062 mmol) were flushed under argon and dissolved in anhydrous toluene (15 mL). 4-Methoxybenzylamine (314 µL,

2.42 mmol, d = 1.057 g/mL at 25°C) and 1,8-diazabicyclo[5.4.0]undec-7-ene (600 µL, 4.00 mmol, d = 1.018 g/mL at 25°C) were added sequentially; the reaction vessel was then sealed and heated to gentle reflux (~110°C). After stirring at reflux overnight, the reaction was cooled to room temperature and diluted with DCM (15 mL). The solution was then passed through a celite filter and the resulting solution was washed with brine (100 mL) and extracted with DCM (3 X 100 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed. The crude residue was purified via flash silica column chromatography using a 1:99 methanol/DCM eluent. The pure desired product was collected and the solvent removed to afford the title compounds as a white solid (52 mg, 8% yield).

1 H NMR (400 MHz, CDCl3) δ 7.39-7.34 (m, 2H), 7.29 (s, 2H), 6.86-6.81 (m, 2H), 4.74

(s, 2H), 3.98 (s, 6H), 3.77 (s, 3H).

13 C NMR (100 MHz, CDCl3) δ 168.3 (2C), 159.1, 153.8 (2C), 129.9 (2C), 129.0, 125.6

(2C), 113.9 (2C), 105.3 (2C), 56.6 (2C), 55.2, 41.0.

111

1,2-Dibromo-4,5-dimethoxybenzene (87)

1,2-Dimethoxybenzene (3.19 mL, 25.0 mmol, d = 1.084 g/mL at 25°C) was flushed under argon and dissolved in anhydrous dichloromethane (50 mL) and cooled in an ice/water bath (~3°C). A bromine solution (11.0 mL, 55 mmol, 5M in anhydrous DCM) was added dropwise to the reaction (3-5°C). The reaction was then removed from the bath and allowed to warm to room temperature and stir overnight. The reaction was then quenched with saturated aqueous sodium thiosulfate (20 mL) and brine (20 mL). After separating the organic layer, the aqueous layer was extracted with dichloromethane (50 mL). The combined organic extracts were then dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum. The crude solid was then recrystallized from a methanol/ethanol solution (2:1) to afford the title compound as a colorless solid after drying under high vacuum (two crops: 4.80 g, 65% yield).

1 H NMR (400 MHz, CDCl3) δ 7.06 (s, 2H), 3.86 (s, 6H).

13 C NMR (100 MHz, CDCl3) δ 148.8 (2C), 115.8 (2C), 114.7 (2C), 56.2 (2C).

112

MOM alkoxyamine (88)

Compound 72a (0.722 g, 1.91 mmol) was flushed under argon, dissolved in anhydrous DCM (15 mL) and placed in an ice/water bath (~3°C). Hydrazine monohydrate (310 µL, 3.83 mmol, 60% w/w hydrazine) was added dropwise to the reaction and the reaction removed from the bath. After stirring at room temperature for 2 hours the reaction quenched with brine (20 mL) and the mixture extracted with DCM (2

X 20 mL). The combined organic extracts were dried over anhydrous sodium sulfate, filtered and the solvent removed under vacuum to yield a colorless, viscous oil (465 mg,

99% yield).

1 H NMR (400 MHz, CDCl3) δ 7.84 (s, 1H), 7.78 (d, J = 8.1 Hz, 1H), 7.73 (d, J = 8.2 Hz,

1H), 7.44-7.39 (m, 2H), 7.35 (ddd, J = 8.1, 6.8, 1.6 Hz, 1H), 5.50-5.30 (br m, 4H), 5.21

(q, J = 6.4 Hz, 1H), 3.52 (s, 3H), 1.48 (d, J = 6.4 Hz, 3H) ppm

13 C NMR (100 MHz, CDCl3) δ 152.8, 133.7, 133.3, 129.3, 127.6, 126.7, 126.1, 124.8,

124.1, 109.0, 94.3, 77.7, 56.1, 21.3.

113

Methyl donor derivative (89)

Compound 88 (0.260 g, 1.05 mmol) and DMAP (0.128 g, 1.05 mmol) were flushed under argon and dissolved in anhydrous DCM (12 mL) with stirring. Anhydrous pyridine

(0.09 mL, 1 mmol, d = 0.978 g/mL at 25°C) was added to the reaction mixture at room temperature. The reaction flask was then placed in an acetone/dry ice bath (-60°C) and methanesulfonyl chloride (0.12 mL, 1.56 mmol, d = 1.48 g/mL at 25°C) was added dropwise to the solution while stirring (-60°C). After stirring for 30 minutes, the reaction was removed from the cold bath and allowed to warm to room temperature. After stirring for 4 hours, the reaction was then quenched with aqueous CuSO4•5H2O (10 mL) and the aqueous layer extracted with ethyl acetate (3 X 15 mL). The combined organic extracts were dried over anhydrous sodium sulfate and the solvent was removed under vacuum.

The crude residue was then purified via flash silica column chromatography using base- treated silica and a 30:70 ethyl acetate/petroleum ether eluent to afford the title compound as a yellow oil after drying under high vacuum (0.130 g, 38% yield).

1 H NMR (400 MHz, CDCl3) δ 7.80-7.71 (m, 3H), 7.47-7.41 (m, 2H), 7.36 (ddd, J = 8.0,

6.8, 1.2 Hz, 1H), 6.91-6.83 (br s, 1H), 5.68 (q, J = 6.8 Hz, 1H), 5.34 (s, 2H), 3.52 (s, 3H),

3.08 (s, 3H), 1.61 (d, J = 6.8 Hz, 3H).

114

Target Donor and N-MOM byproduct (36 & 92)

Compound 88 (273 mg, 1.10 mmol) was flushed under argon and dissolved in anhydrous DCM (15 mL) with stirring. Anhydrous N,N-diisopropylethylamine (0.29 mL,

1.65 mmol, d = 0.757 g/mL at 25°C) was added dropwise to the reaction at room temperature. After cooling the reaction in a dry ice/acetone bath (-60°C), trifluoromethanesulfonic anhydride (0.22 mL, 1.32 mmol, d at 25°C = 1.677 g/mL) was added dropwise to the reaction. After stirring for 2 hours (-60°C) the bath was removed and the reaction was allowed to warm to room temperature. After stirring overnight the solvent was removed under vacuum and the crude residue was purified via flash silica column chromatography using a 15:85 ethyl acetate/petroleum ether eluent. Two different compounds were separately isolated. The N-MOM protected derivative, a yellow tinted oil

(160 mg, ~38%) and the desired product with some small impurities (169 mg, ~46% yield).

A portion of the crude residue (60 mg) was then purified using a silica plug. The plug was washed with a series of solvents: petroleum ether (200 mL), 10/90 ethyl acetate/petroleum ether (100 mL), 25/75 ethyl acetate/petroleum ether (100 mL). The final compound was obtained as an orange oil (10 mg).

115

Product 36

1 H NMR (400 MHz, CDCl3) δ 7.80-7.73 (m, 2H), 7.67 (d, J = 8.0 Hz, 1H), 7.45 (ddd, J =

8.4, 6.8, 1.2 Hz, 1H), 7.36 (ddd, J = 8.4, 6.8, 1.2 Hz, 1H) 7.19 (s, 1H), 5.60 (q, J = 6.8

Hz, 1H), 1.72 (d, J = 6.8 Hz, 3H).

13 C NMR (100 MHz, CDCl3) δ 151.6, 134.5, 129.1, 128.6, 127.9, 127.5, 127.1, 126.0,

124.2, 119.4 (q, J =323 Hz) 111.1, 83.0, 19.0.

19 F NMR (376 MHz, CDCl3) δ -73.48.

Product 92

1 H NMR (400 MHz, CDCl3) δ 7.83 (br s, 1H), 7.80-7.71 (m, 3H), 7.47-7.41 (m, 2H), 7.38

(ddd, J = 8.0, 6.8, 1.2 Hz, 1H), 5.71 (q, J = 6.4 Hz, 1H), 5.36-5.32 (m, 2H), 3.52 (s, 3H),

1.61 (d, J = 6.4 Hz, 3H) ppm

13 C (100 MHz, CDCl3) δ 152.6, 134.1, 130.2, 128.9, 127.6, 126.80, 126.76, 126.1, 124.5,

119.4 (q, J = 323 Hz) 109.4, 94.5, 81.0, 56.3, 20.1.

19 F NMR (376 MHz, CDCl3) δ -73.11*.

Note: Pyrollidine impurities are observed in NMR spectra because these spectra were obtained with an sulfonylation using pyrollidine.

116

Photolysis of Donor 36

Donor 36 (~0.45 mg, 1.3 µmol) was dissolved in anhydrous CD3CN (320 µL) and phosphate buffer (480 µL, 0.10 M, pH 7.00) with trisodium phosphate as an internal reference standard under an argon atmosphere. The solution was then transferred to an

NMR tube which was fitted with a J-yuong air-tight cap. The sample was irradiated using a Rayonet mini-photoreactor with 350 nm bulbs (4 W, 8 lamps). The sample was periodically analyzed (0, 1, 2, 3, 5, 10 and 15 minutes) by 19F NMR and 1H NMR

19 - spectroscopy. Integration of F NMR signals showed that the ratio between CF3SO2

/CF3SO2NH2 products was approximately 28:72.

- 19 CF3SO2 : F NMR (376 MHz, CD3CN) δ – 87.91 ppm

19 CF3SO2NH2: F NMR (376 MHz, CD3CN) δ – 80.34 ppm

117

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122

NMR SPECTRA

1H NMR of 2,3-TIPS ester (18)

13C NMR 2,3-TIPS ester (18)

123

1H NMR 2,3-TIPS 1 alcohol (19)

13C NMR 2,3-TIPS 1 alcohol (31)

124

1H NMR 2,3-TIPS aldehyde (31)

H2O

13C NMR 2,3-TIPS aldehyde (31)

125

1H NMR of 2,3-TIPS 2 alcohol (32)

13C NMR of 2,3-TIPS 2 alcohol (32)

126

1H NMR of 2,3-TIPS Mitsunobu (33)

13C NMR of 2,3-TIPS Mitsunobu (33)

127

1H NMR of 2,6-TIPS ester (38)

1H NMR of 2,6-TIPS alcohol (39)

EtOAc EtOAc

128

1H NMR of 2,6-TIPS aldehyde (40)

(CH3)2CO

1H NMR of 2,6-TIPS alcohol (41)

EtOAc EtOAc

129

1H NMR of 2,6-TIPS Mitsunobu

H2O

130

1H NMR of 3,3’-di-tert-butyloxaziridine (49)

13C NMR of 3,3’-di-tert-butyloxaziridine (49)

131

1H NMR of 4-Nitro-N-hydroxyphthalimide (67a)

H2O

(CH3)2CO

13C NMR of 4-Nitro-N-hydroxyphthalimide (67a)

132

1H NMR of 4,5-dichloro-N-hydroxyphthalimide (67b)

H2O

13C NMR of 4,5-dichloro-N-hydroxyphthalimide (67b)

133

1H NMR MOM ester (68a)

H2O

13C NMR MOM ester (68a)

134

1H NMR of MOM 1 alcohol (69a)

EtOAc EtOAc

13C NMR of MOM 1 alcohol (69a)

135

1H NMR of MOM aldehyde (70a)

13C NMR of MOM aldehyde (70a)

136

1H NMR of MOM 2 alcohol (71a)

(CH3)2CO

13C NMR of MOM 2 alcohol (72a)

137

1H NMR PMB ester (68b)

H2O

13C NMR of PMB ester (68b)

138

1H NMR of PMB 1 alcohol (69b)

H2O

13C NMR of PMB 1 alcohol (69b)

139

1H NMR of PMB aldehyde (70b)

H2O

(CH3)2CO

13C NMR of PMB aldehyde (70b)

140

1H NMR of PMB 2 alcohol (71b)

(CH3)2CO

13C NMR of PMB 2 alcohol (71b)

141

1H NMR of SEM ester (68c)

H2O

13C NMR of SEM ester (68c)

142

1H NMR of SEM 1 alcohol (69c)

(CH3)2CO

13C NMR of SEM 1 alcohol (69c)

143

1H NMR of SEM aldehyde (70c)

13C NMR of SEM aldehyde (70c)

144

1H NMR of 2 SEM alcohol (71c)

13C NMR SEM 2 alcohol (71c)

145

1H NMR of TBS ester (68d)

13C NMR of TBS ester (68d)

146

1H NMR of TBS 1 alcohol (69d)

(CH3)2CO

13C NMR of TBS 1 alcohol (69d)

147

1H NMR of TBS aldehyde (70d)

13C NMR of TBS aldehyde (70d)

148

1H NMR of TBS 2 alcohol (71d)

13C NMR of TBS 2 alcohol (71d)

149

1H NMR of MOM Mitsunobu (72a)

(CH3)2CO H2O

13C NMR of MOM Mitsunobu (72a)

150

1H NMR of PMB Mitsunobu (72b)

13C NMR of PMB Mitsunobu (72b)

151

1H NMR of SEM Mitsunobu (72c)

13C NMR of SEM Mitsunobu (72c)

152

1H NMR of TBS Mitsunobu (72d)

13C NMR of TBS Mitsunobu (72d)

153

1 H NMR of MOM Mitsunobu NO2 (73)

13 C NMR of MOM Mitsunobu NO2 (73)

154

1 H NMR of MOM Mitsunobu Cl2 (74)

13 C NMR of MOM Mitsunobu Cl2 (74)

155

1 H NMR of SEM Mitsunobu NO2 (75)

13 C NMR of SEM Mitsunobu NO2 (75)

156

1H NMR of 1,2-Diiodo-4,5-dimethoxybenzene (84)

H2O (CH3)2CO

13C NMR of 1,2-Diiodo-4,5-dimethoxybenzene (84)

157

1H NMR of PMB-phthalimide (86)

H2O

13C NMR of PMB-phthalimide (86)

158

1H NMR of 1,2-Dibromo-4,5-dimethoxybenzene

H2O

13C NMR of 1,2-Dibromo-4,5-dimethoxybenzene

159

1H NMR of MOM alkoxyamine (88)

13C NMR of MOM alkoxyamine (88)

160

1H NMR of Donor (36)

13C NMR of Donor (36)

161

19F NMR of Donor (36)

1H NMR of N-MOM (92)

162

13C NMR of N-MOM (92)

19F NMR of N-MOM (92)

163

19F NMR of photolysis of 36 at 0 minutes

19F NMR of photolysis of 36 at 15 minutes